FORMATION MECHANISM OF EAR PLUG IN BALEENWHALES IN RELATION TO GLOVE-FINGERTADAYOSHI ICHIHARAINTRODUCTION

Since the important paper of the ear plug in the Mysticeti was contributed by Purves (1955), the relations between the ear plug laminationand the other valuable age characters have been researched in several
papers, Laws & Purves (1956), Nishiwaki (1957), Symons & Weston(1958), Nishiwaki, Ichihara & Ohsumi (1958) and Purves & Mountford(1959). In particular the valuable suggestions are given in the last two
papers which are described based on a great numbers of ear plug fromthe fin whale. The comparisons of the biological information from thelamination counting with that from the baleen plate reading in theyoung stage and with that from the corpora counting in the ovary offemale whale have confirmed the validity of lamination numbers of ear
plug for the age determination as seen in the papers mentioned above.
However, the accurate rate of annual increment of laminae is necessary to advance the whale biology and it finally should be checked by
the marking experiment and so on to avoid the interpretation favoured
by individual scientists.
As another approaching method to know the increment rate, it remains the fascinating problem when the alternation of the dark andlight band occurs in the plug core in response to the internal physiological rhythm of whale body. In the course of study on this subject, it
was necessary that the glove-finger and the ear plug were examined
in detail morphologically and histologically. In this paper the several
supplemental informations for the previous works are obtained from theexternal observation of the glove-finger and the ear plug. With regard
to the formation mechanism of ear plug, new findings are given fromthe histological study. Any conclusive comment is not given in thispaper to the reason why the alternation of bands occurs in the ear
plug. Such a reason should be explained in the future research.
I am indebted to Dr. Hideo Omura, the Director of our Institute, for his
encouragement throughout this work. My sincere thanks are due to Dr.
Hiroshi Hosokawa and Mr. Toshitomo Shida, the Department of Anatomy,
Faculty of Medicine, University of Tokyo, for their kind helps andvaluable suggestions in the histological study. I am also indebted to
107

108

T. ICHIHARA

the inspectors and the staffs of the whaling companies, too numerous
to name here, who collected many materials for the Whales ResearchInstitute.
MATERIAL AND METHOD

Numerous ear plugs have been collected on the deck of the Japanese
floating factory ships in the Antarctic Ocean and the northern part of
the North Pacific since 1956. Fin whale plugs occupied the most partof these specimens which were preserved in 10% formalin solution soonafter collection. The ear plugs from the blue, humpback and sei whale
were preserved in the similar way. The humpback whale plugs off
Okinawa Island were collected from January to April in 1959. A few
specimen from the Bryde's whale and the minke whale also have obtained from the Japanese coastal land stations, with the fin whale plugs
from the East China Sea.
Although the laminations of all plugs were counted, the morphologicalstudy in this paper mainly dues to 662 fin whale plugs from the northern part of the North Pacific in 1957 and 1958. Under the imperativenecessity of explanation, the numbers were complemented by the plugs
from the fin whale in the other waters and from the other species.
With these ear plugs, the glove-fingers were collected from thevarious whales of different localities but they are in less numbers thanthe ear plugs. 165 glove-fingers were used for the present purpose.
In the present histological study, the blocks of specimens from thevarious species were embedded in paraffin in the first trial, however,this method was not suitable for the preparation of section. Therefore,
the blocks of specimens were prepared in the celloidin and frozen section in the second step. Finally the celloidin section suited for the
hard materials like the glove-finger and the frozen section did for thesoft materials like the ear plug. In such ways, the various parts fromthe specimens were sectioned in the thickness from 10 to 15 µ.
After sectioning the specimens, the several staining methods weretried; haematoxylin eosin, Heidenhain's iron haematoxylin, AZAN, SUDAN
III etc. In particular, haematoxylin eosin and SUDAN III staining wereapplied for the study on the formation mechanism of ear plug. Photomicrographs were taken from the numerous sections and some of them
are illustrated in plates.
SIZE AND TYPE OF GLOVE-FINGER

Penetrating the thick blubber, the external auditory meatus of theEAR PLUG IN BALEEN WHALES

109

baleen whales goes along the squamosal region of the skull, endingat the glove-finger structure connecting the tympanic bulla with thetriangular ligament. Glove-finger had been believed by many whale
biologists as the tympanic membrane until Fraser & Purves (1954) havesuggested th8,t in the course of study on the conductivity of sound, thetriangular ligament mentioned above corresponds to the tympanic membrane. In baleen whales, the glove-finger projects outerwards into theexternal auditory meatus, having the slightly flattened shape in verticaldirection and the elongated, hollow conical structure in general. At
its outer convex end it is capped by the ear plug. Its position and its
relation to the ear plug were illustrated concretely in text-figure 1 in
Purves' paper (1955). Since the glove-finger is closely associated withthe formation of ear plug in the auditory meatus, it is necessary tonote glove-finger first of all remarks on the shape of ear plug.
In the course of taking the ear plug from the whale head, it is often
detached from the outer surface of glove-finger. This detachment, being
usually seen more frequently in the young whale than in the old one,sometimes depends on the plug shape coating the curved, extremity ofglove-finger and sometimes to the shape of papillary layer existing in the
corium of glove-finger. The numerous papillaries often project from theouter surface of glove-finger to enter the column of tissue of the ear
plug. Detailed description on this connection appears later in this paper.
The thick membrane-like glove-finger shows usually the white, yellowish
white colour and sometimes the slightly smoke-stained white colour. In
the longitudinally bisected specimen many capillaries are seen embossedon the internal surface of the glove-finger. This observation implies
presumably the abundant blood vessels exist in the glove-finger.
On the size of glove-finger several descriptions have seen until now.
Kellogg (1928) has stated that the glove-finger of humpback whale is
3 1 / 2 inches long and it is flexible in the fresh material. It has been
described by Hinoura (1938, '41, '43) that the thickness and size of themembrane-like glove-finger is a little different from species to species,
however, it is from 2.0 mm to 5.0 mm thick in the various baleen whales.
He has furthermore concluded comparing the sizes of glove-fingers from
5 species in baleen whales that the minke whale and sei whale possess
the glove-finger of about the same size, 5.0 cm in length, and the fin
and blue whale have a little more large ones and at any rate the humpback whale possesses the most large one of 8.0 cm in length and3.0 cm in the greatest breadth. Yamada (1948) has shown the glovefinger projects outerwards about 6 cm into the external auditory meatus
in the Antarctic fin whale, In Burne's cetacean dissection (1952) it has

T. ICHIHARA

110

been suggested the glove-finger in large baleen whale some 2 1/2-3 inches
long in the protruding part.
Fig. 1 indicates a close relationship between the length of projected
glove-finger from the tympanic bulla and its greatest breadth. Mostof examined specimens consist of 53 fin whales from various localities
and their mean values are indicated in the left side, suggesting thelinear relationship is suitable in two kinds of measurements. Records
from one northern blue whale, one humpback whale from Okinawa
waters and one Bryde's whale from the coast of Japan also are plotted,
being situated near the straight line. Furthermore to the right side

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Fig. 1. Relation of length and weight to greatest breadth of glove-finger. Length
indicates the projected part from the tympanic bulla. Fin whale, mean values;
other species, single records. e Fin whale, x Blue whale, O Humpback whale,
6. Bryde's whale.

in Fig. 1 mean glove-finger weights at different greatest breadth areplotted on a double logarithmic scale for the fin whale. Records fromblue, humpback and Bryde's whale are added near the assumed straightline. Although the small numbers of records give a great variation in
the lower range, the linear relationship between the weight of glovefinger and its greatest breadth is assumed. In the examined specimen,
the maximum length of glove-finger is 84.8 mm and its minimum lengthis 51.0 mm. The range of weight covers 31.4 gr from 7.5 gr, four times
increase as compared with a less than twice increase in the. greatest
breadth (22.4 mm to 42.4 mm). The mean thickness of membraneous
glove-finger is 3.17 mm for 21 fin whales, being 3.16 mm for 5 blue
whales and it is 3.50 mm for 8 humpback whales, however, these values
do not seem to be so accurate since the measurement is difficult in the

111

EAR PLUG IN BALEEN WHALES

specimens of markedly projected pappilae. The thickness varies fromone specimen to another and its range is from 2.0 mm to 5.0 mm.
In general my finding for the size of glove-finger is compatible withthe previous works mentioned above, however, it must be emphasizedthat all findings in the previous paper are due to the small numbers ofglove-finger. Hinoura is the first person who has compared the sizesof glove-finger from various baleen whales as far as I know. His finding should be corrected in respect of the ranking of size. I disagreewith his interpretation on the minke whale examined, judging from theexternal character of that whale.

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Fig. 2. Relation between greatest breadth of glove-finger and age of fin whalein three localities. x East China Sea, 0 Northern Pacific, e Antarctic.

In relation to the life-history of whale, Purves (1955) has suggested
that in view of its association with the tympanic annulus and its importance in regulating the tension of the tympanic ligament, it may be
assumed that the glove-finger also remains constant in size throughout
the life of the animal. Certainly Purves' suggestion must be taken up
here and confirmed, because there is a close association between thesize of outer part of the glove-finger and the size of core of the ear
plug. In this connection, the study is started from whether the sizeof glove-finger changes or not at the increasing age of whale. Since
the glove-finger shows the curious form, it is so difficult to express
its size as dimensions. So far as the breadth of core of ear plugconcerns, the greatest breadth of glove-finger becomes the best expression in dimensions. With regard to the age of whale, there is no justification to reject the lamination number seen in the plug core is an
excellent age character according to Nishiwaki, Ichihara & Ohsumi

T. ICHIHARA

112(1958), Purves & Mountford (1959), even if no method has yet beenstandardised on the annual increment of lamination as Chittleborough &Godfrey (1957) and Symons & Weston (1958) have pointed out.
In Fig. 2 the greatest breadth of glove-finger is plotted against thelamination number. The specimens used here are collected from the fin
whales in three localities-the East China Sea in 1958, the northern partof the North Pacific in 1957 and the Antarctic Ocean between 1956 and1958. In the range from 3 to 80 of lamination, the greatest breadth
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Fig. 3. Frequency distribution of greatest breadth of glove.finger. The means
and two standard errors are indicated. Above: On the fin whale in three localities, x x East China Sea, 0- - -0 Northern Pacific, • - • Antarctic.
Below: On the other baleen whales, O- - -O Okinawa humpback whale, • - •Northern Pacific blue whale, & Northern Pacific sei whale, 6 Bryde's whale,x Minke whale.

of glove-finger does not show the increasing character with age, varying from one specimen to another. This fact implies the glove-finger
remains constant for one species from the birth to the end of whale
life, confirming Purves' suggestion. It is of interest to note the fin
whale of the East China Sea possesses smaller glove-finger than thoseof the North Pacific and the Antarctic. It is interesting incidentallythat the breadth of glove-finger does not show the significant difference
between the male and the female fin whale in one locality, and it isfound conclusively in the other baleen whales.

EAR PLUG IN BALEEN WHALES

113

Since a morphological character of constant size, in no relation to theincreasing age, often becomes a clue to the study of subpopulation, I
collected the glove-finger from the various baleen whales to measureits greatest breadth. The frequency distributions of the greatest
breadth are found in Fig. 3 in which the means and two standard
errors are indicated for each group of whale. Since the data containthe glove-finger from of which ear plug is detached and missed, thenumbers of specimens become a little larger as shown in Fig. 3 thanin Fig. 2. On the fin whales as explained in the figure, the breadthfrom the North Pacific group is in almost the same range as that fromthe Antarctic group. In this group the breadth is 33.7±1.54 mm (means
and two standard errors) and in that group it is 33.3±0.74mm. It isevident no significant difference is found between both group. While,in the East China Sea group the breadth is as small as seen in the
figure and 28.2 ± 0.99 mm, being different significantly from the othertwo groups. It has been pointed out by Mizue (1956) that the fin whale of
the East China Sea matures sexually at the smaller size than that of thenorthern part of the North Pacific by about 2 feet. Besides Mizue &Fujino (1957) have suggested the shape of baleen plate is different between
both areas. Furthermore Ichihara (1957) have concluded that the external
shapes of the whales from both areas are significantly different andsuggested that the fin whales are divided from the external proportion
into two areas with mathematical foundation. Occurrence of smalJer
glove-finger in the East China Sea may be taken as the other explanationon the locality of the fin whales there in addition to findings mentioned
above, and on this subject further studies of subpopulation are needed
as pointed out by Omura, Fujino, Ichihara, Kimura (1958).
Since the collections of glove-fingers from the other baleen whale are
not so large, their distributions are seen as the frequency number inthe lower part of Fig. 3, in which the means and two standard errors
are indicated for the northern Pacific blue whale and for the humpback
whales near Okinawa Island where the whaling has been operated in
the winter season since 1958. In the group from 5 blue whales, thegreatest breadth of glove-finger is 35.6 ± 5.12 mm and in the groupfrom 16 humpback whales it is 27.5±2.24mm. It is suggestible fromthese means and two standard errors that the breadth differs significantly between these two groups, although the indicated specimen issmall in number and the overlapping area is seen between two frequency distributions. Kawakami & Ichihara (1958) has made clear fromthe evidence of whale marking that the humpback whales off Okinawa
Island migrate as far as Alaskan waters in the north-eastern part of

114

T. ICHIHARA

North Pacific. Accepting this clearness the glove-finger of the humpback whale living in the northern part of the North Pacific is inferred
to be the same in its greatest breadth as that of the Okinawa humpback whale.
The frequency distribution of glove-finger of the humpback whaleshows seemingly the bimodal curve, which is based on the small
numbers of materials collected. As regards the sei whale and Bryde's
whale, the only one glove-finger is obtained from the adjacent waters
to Japan and its breadth is as medium as 30.7 and 27.7 mm respectively.
One specimen from the minke whale captured in the Okhotsk Sea is as
small as 20.9 mm in its breadth. The glove-finger of blue whale seems
to be a little larger than that of the fin whale.
In relation to the shapes of laminae seen in the ear plug, the typeof glove-finger must be noticed. The present type of glove-finger isdependent upon the shape of papillae seen in its corium. In the course of
study on the glove-finger of blue whale, the great numbers of papillae
are observed in naked eyes to project remarkably outerwards from its
surface. All examined specimens from the blue whales have the protruding papillae of which parts are as long as about 5 mm and marked
at the curved extremity of glove-finger. These papillae go into thetissue of ear plug covering them, therefore, the ear plug being compacted between one papilla and the neighbouring one. It was described
previously in this paper the detachment of ear plug from the glovefinger partly depended on the shape of papillae layer. This statement
are supported here by the fact that the collected glove-fingers sticking
to the ear plugs usually make the papillae projecting into the plug.
With regards to the glove-finger of fin whale, its type may be divided
into three groups. In the first group, the papillae project conspicuously
outerwards from the surface of glove-finger like the blue whale. In
the second, they project moderately and are not so many in numbers
as in the first group. In the third group, they are not so protrudentthat the surface of glove-finger looks smooth. These three types ofglove-fingers from the fin whales are shown in Plate I, Fig. 1 withthe glove-finger from the other baleen whale. The curvature of the
distal end of glove-finger effects on that of the laminae of ear plug,varying from one specimen to another, however, it is effectless on thetype of glove-finger. According to the grouping method into three
types the percentage of the first group is as low as 13.4 and that of
the second group is as medium as 32.8, that of the third group being
as high as 53.8, in 89 glove-fingers from the northern Pacific fin whales.
These percentages show the papillae of the fin whale glove-finger usually are not so protrudent as those of the blue whale. This finding

EAR PLUG IN BALEEN WHALES

115

may be supported from the view of the proximal end of ear plug as
indicated in Fig. 4.
In the most case of ear plug collection, ear plugs detach from theouter surfaces of glove-fingers but the borders between both materials
are kept well in the formalin preservation. From the detailed observation it is confirmed that the epithelium of glove-finger remains at theproximal end of ear plug, where the type of papillae of glove-finger
are observed indirectly. Supplying the small numbers of the glovefingers, 662 ear plugs from the North Pacific expeditions in 1957 and1958 are used for this survey and the percentage frequencies of three
types are plotted against the lamination numbers in Fig. 4. The second
Number of specimens examined

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Fig. 4. Percentage frequency of three types of fin whale glove-finger observed
indirectly from ear plug, at increasing lamination number. • - • papillae
not projected, x- - - x medium type, 0 - 0 papillae projected markedly.

type occupies about 30 percentages in all specimens and the comparatively constant level from the young to the old. While the first typeof the remarkably projected papillae shows the percentage below 20 in
the young and characteristically indicates increasing percentage fromthe young to the old. With regard to the third type, its percentage
falls with the increasing age to the contrary of the increasing percentage in the first group. Over 50 laminations, the first and third group
approach to the second group in their percentage. This interestingfinding suggests the projection of papillae of glove-finger grows higher
and higher from the young to the old and finally three types occur inalmost the same frequencies in old whales. It is supported by theshapes of laminae seen in the core of ear plug as described later, how-116

T. ICHIHARA

ever, the occurrence of the first type in the very young whale should
be noted.
In the one specimen from the sei, Bryde's and minke whale respectively, the papillae are not protrudent, belonging to the third group.
Three types appear in the glove-fingers of humpback whale like thoseof the fin whales. In all specimens examined from the blue whale, thefin whale and the humpback whale, the occurrences of papillary types
are almost similar in the two sexes.
RELATIONSHIP BETWEEN CORE LENGTH AND SKULL WIDTH

It has been suggested by Purves (1955) "the characteristically great
lateral growth of the posterior region of the skull in the Mysticeti isapparently almost wholly associated with the lateral extension of thezygomatic process of the squamosal, the paroccipital process and the
mastoid process of the tympano-periotic and during the lateral extension of these bones which are concerned in the formation of the bonyexternal meatus, the wax plug would tend to be drawn away from its
contact with the glove-finger." Later Laws & Purves (1956) have explained " the dark band found in the fin whale plug marks an abrupt
interruption which implie almost complete cessation in the growth ofthe entire skull and presumably in that of the skeleton and such aninterruption, therefore, would have occurred during the migratory period
when the excessive physiological demands of active swimming werecoincident with complete absence of food." Apart from whether the darkband of core is formed or not coincidentally with the migratory period,
between these two suggestions mentioned above it is a common maintenance that the formation of ear plug is dependent on the various
stages of the lateral growth of skull. If so, these important suggestions must be confirmed through the relation between the core lengthand the skull width.
In the northern Pacific expedition of 1957, I measured the several
parts of skull of the fin whale and simultaneously collected the ear
plug from the measured whale. Two purposes have lain in these skull
measurements, in which one purpose is to contribute through the craniometry to the study on subpopulations of fin whales and the other is
to confirm the relationship between the formation of ear plug and thelateral growth of skull. For the latter purpose two dimensions of skull
took place before sawing the bone. One dimension is the greatest widthof skull and the other is the distance between both postglenoid processesof squamosal. The greatest width of skull means the distance between
both zygomatic process of squamosal which is situated in the adult fin

EAR PLUG IN BALEEN WHALES

117

whale at a little anterior part than the tymanic bulla and the external auditory meatus. The external auditory meatus proximally lies
in a deep groove between squamosal and paroccipital process and therefore the distance between both postglenoid processes of squamosal will
become better expression of the width of skull near the external auditory meatus.
With regard to the relationship between the lamination number andthe core length of fin whale plug, Nishiwaki, Ichihara & Ohsumi (1958)
have concluded that the total length of the core per one lamination
varies very greatly from one specimen to another. This conclusion was
also affirmed later by Purves & Mountford (1959) using many ear plugs
from the Antarctic fin whales. If this great individual variation of the

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Fig. 5. Relation of length of plug core to greatest width of the skull infemale fin whale. Individual value is indicated.

total length of core is depend on the ratio of lateral growth of individual skull, the close relation should be found between the total lengthof core and the width of skull. To confirm this relationship two parts
from 69 skulls of female fin whales are plotted corresponding to thetotal length of core in Figs. 5 and 6, in which the total length of coreper the skull width varies greatly from one specimen to another, however, the hypothesis of a linear relationship between the total lengthof core and the skull width provides a fit to the data in the range ofskull width indicated. The linear regression of the total length of coreto the greatest width of skull is
Y=0.21-9.67X

and to another width of skull it is
Y=0.29-15.lOX

where Y and X are the total length of core in mm and each skull width

T. ICHIHARA

118

in cm respectively. From this result it can not be emphasized that
there is a close association between the increasing total length of core
and that of the skull width. The similar result is obtained when thecorrelation coefficients are considered for 51 measured male fin whales
reserved from Figs. 5 and 6. In male fin whales, the greatest widthof skull ranges from 170 to 230 cm and another width of skull ranges
from 130 to 190 cm respectively.
The correlation coefficient between the total length of core and thegreatest skull width is as little as 0.43 and that between the total
length of core and another skull width is as little as 0.40 in male fin
whales. Then the coefficients are as little as 0.33 and 0.36 for eachskull width of the female fin whale. Using t-test, these correlation co-

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Fig. 6. Relation of length of plug core to distance between both postglenoid process of squamosal of the skull in female fin whale. Individual
value is indicated.

efficients are significant at the level between 1% and O.lo/o respectively,
however, it will be beside the mark to emphasize the close correlation
between the increasing total length of core and the growing skull width.
Because these significancies derived from the mathmatical treatment do
not become justifiable reasons to conclude that there is a close causality
between two variates although the interrelationship should not be neglected.
Recently Purves & Mountford (1959) have inferred that the total
length of ear plug has no close relationship to the skull length. It is
assumed that their inferrence does not come from the direct research
for the relation between the plug length and the skull width but it isbased on the combination of the next two findings: firstly, there is a
close linear relationship between the body length of whale body and theskull width, secondly, between the body length and the core length isEAR PLUG IN BALEEN WHALES

119

there a relationship which is perceived between the lines in their paper.
That is, my finding may be taken as a definite illustration of their inferrence. The increasing length of core should be positively based on
the internal progressing metabolism of whale body as stated by Purves& Mountford (1959), and this finding will be explained later in this paper.
It is of incidental interest to note that the increasing rates of thetotal length of core on two parts of skull width for female and male
fin whales are not significantly different. Furthermore the distance
between both postglenoid processes of squamosal is not deemed to effectmore positively on the increasing length of core than the greatest withof skull.
GENERAL NOTE ON PLUG CORE

Since the laminae in the conical ear plug are deposited from the epithelium of glove-finger in the progressive stage of the life of baleen
whale, the total length of core seems to be stretched regularly fromthe young to the old age. Purves (1955) has indicated the thicknessof the laminations decreases exponentially over the greater part of theseries, although there is a certain degree of irregularity. With regard
to this irregularity Laws & Purves (1956) have suggested in their preliminary report the alternation in the thickness of the fin whale lamina
may be thought to cast some doubt on the validity of assesing a regular
six monthly period for the formation of each lamination and the interlamina areas of the ear plug would occur at six monthly intervals inthe blue whale and approximately four and eight monthly periods inthe fin whale, considering the migration periods exist regularly in theblue whale and irregularly in the fin whale. However, it must be emphasized that the alternation in the thickness of lamina often occurs
irregularly in the blue whale ear plugs I examined.
It is of interest to note the finding in their paper the first lamination, being always a small, conical, unstratified body rich in calcium, isdeemed to be that part of the plug which is present in the ear before
birth. The prenatal lamina is always present in all ear plugs I examined,
its structure and thickness varying from one specimen to another. In
the young ear plug its presence is confirmed more easily than in theold one. This phenomenon is explained from the fact that the epithelium of glove-finger is fully keratinized in the distal end of the old ear
plug and the conical form of the first lamination is compressed between
the growing core and the interfering outer covering derived from theexternal auditory meatus. The presence of core before birth is suggested by the evidence that a full grown foetus of the humpback whale

120

T. ICHIHARA

caught off Okinawa Island in the winter season of 1959 has the thin
ear plug in the outer surface of the glove-finger. This male foetus is
12 feet and 10 inches long, it being considered to be near the lengthof parturition (Nishiwaki, 1959). In this connection it is interesting to
draw attention to the occurrence of the ceruminous glands in the humanfoetus. Iwata (1933) have reported the ceruminous glands of humanfoetus in 6 months of pregnancy begin to secrete as the apocrine glands,
however, there are controversies
on the embryological studies of theceruminous glands according toNagashima (1934), Hirota (1939),
Nagasawa (1941) and Ito (1942,'49). Purves (1955) has proposedthat the many ceruminous glands
exist in the curved extremity ofglove-finger, but, for reasons statedlater in the histological study ofear plug, I disagree with this interpretation. Apart from the presenceof ceruminous glands in the glovefinger of the baleen whale, theembryological study of ear plugremains a further important one.
There has been no description
with regard to the breadth of coreof the ear plug in relation toYoung plug
Old plugthe constant size of glove-finger
Fig. 7. Diagram showing the increasing length throughout the life span of whale.
and breadth of ear plug core from the young
In the course of the ear plugto the old age with the directions of pressures. OC: outer covering of the ear plug, study, I noticed the young plug
C: core of ear plug, GF: glove-finger, Silid was different in its shape fromarrows show the breadth of core and pres- the old plug. The difference issure in its part. Broken arrows show themore evident in the specimen of
longitudinal and lateral pressures.
which ear plug sticks on the glove
finger and it is shown in two diagrams of Fig. 7. Although the all ear
plugs cover the distal part of the curved glove-finger, the young plugcharacteristically caps the curved extremity of the glove-finger, while
the old plug usually covers the almost all curvature of glove-finger.
The first lamina of the humpback whale foetus mentioned above caps
only the curved extremity of its glove.,.finger. The fringe of old ear plug
existing along the lateral side of glove-finger is really composed of both

EAR PLUG IN BALEEN WHALES

121

the core part and the outer covering part.
The breadths of large numbers of ear plugs from the North Pacific
fin whale are measured in such a right-angled direction to the lengthof core as indicated in Fig. 7. These breadths of cores are plottedagainst the lamination numbers in Fig. 8 in which each plot shows themean breadth per 2 laminations. For this purpose, 437 specimens fromthe fin whale are used and the numbers of specimens per 10 lamination
numbers are described in Fig. 8. The breadth of core varies from one
specimen to another, growing from the young to the old, however, overabout 40 laminations it does not grow more. It is of interest that themean breadth of core a remarkably similar in the two sexes, concequently the specimens from both sexes are applied in Fig. 8. Nishiwaki,
Ncvnber oF specimens examined

104

112

80

68

31

10

20

4

40
E
E
.!:

..• ...

30

•

@

8
'-'0

20

-£
-u

"'~

co

10
10

20

30

40

50

60

7.0

80

Lamination ·number

Fig. 8. Change in the breadth of plug core at increasing lamination numbers in
the northern Pacific fin whale.

lchihara & Ohsumi (1958) and Purves & Mountford (1959) have concluded
the increasing rate of the core length is not different between the maleand female fin whale. The size of core finally is resemble in the twosexes of the fin whale and this finding presumable is extended to allbaleen whales.
The presence of longitudinal light bands running in the core are themost evident macroscopically in its centre portion and the distance between one longitudinal light band and the neighbouring is the most wide
there in all areas of core. It should be noticed further more that thebreadth between two bands spread a little and the numbers of longitudinal light bands are increasing little by little from the distal to theproximal end of plug core. The latter finding suggests in the old individual the ear plug are not only formed from the curved extremity
but also from the lateral side of glove-finger. It is suggested that the122

T. ICHIHARA

outer covering derived from the lining of the meatus presses little bylittle the lateral side of the growing plug core from the young to theold.
After all, the conical form of the plug core is deemed to be dependent
upon the balance of the next three pressures, which are indicated inFig. 7. The two pressures of them are due to the keratinized epithelium of the glove-finger, in which the most effective one on the conicalform of core operates in the outward direction from the glove-finger,
the other being in the laterally outward direction from it. The lastpressure is due to the compacted keratinized epithelium of the meatus
and operates in the laterally inward direction from it. The various
conical form of the ear plug results from the three pressures mentioned
above, which operate in different intensities from individual to individual.
Among the baleen whale I examined, the longitudinal pressure is more
intensive in the plugs of the blue, fin and humpback whales than inthat of the sei whale. In the sei whale the distance between two laminations regarded as the age character is usually narrower. Plate I,
Fig. 2 indicates the bisected ear plugs from the different 5 baleen whales.
It has been concluded by Nishiwaki, Ichihara & Ohsumi (1958) thatthe colour of the plug core in the young fin whale is discriminated fromthat in the old fin whale, and that the colour of core from the sexually
immature whale is rather whitish yellow while that from the old whalechanges from a dull ochre to blackish brown. This finding in the fin
whale is extended to the plug core of the other baleen whale and it issupplemented by the next explanation. The change of colour appears
even in one specimen. The dark band of core is rather lighter in theproximal end than in the distal end, and this suggests that the keratinizing progresses further more in the distal end of core than in theproximal end, following the period elasped since the epithelium is detached from the glove-finger. It must be noted that in the parts ofcore surrounded by the outer covering the darker colour appears macroscopically than in the center of core. Lastly in the supplemental noteon the core colour, it is necessary to describe the abnormal ear plugappears in very few frequency. In this abnormality there are various
cases to be studies further as seen in Plate II, Fig. 1. In the extremely abnormal ear plug, which looks like a black coal, the lamination
number is not counted. In the other case, the alternate occurrences ofthe dark and light band are interrupted abruptly in the series by theblackish brown substances and successively appear the normal laminae.
In some cases the alternate laminae are not seen until the core is sectioned longitudinally.

EAR PLUG IN BALEEN WHALES123

HISTOLOGY

Morphological characters on the glove-finger and on the ear plug havebeen described and suggestive to some extent on the mechanism of ear
plug formation, which should be explained in the histological study. In
this connection the glove-finger is examined firstly since it plays a important part in the formation of ear plug.
Glove-finger. Specimens have been preserved in 10% formalin solution
shortly after they are collected on the factory ships and from the land
station. Most of all specimens examined are composed of the glove:fingers from the fin whale and blue whale and small numbers of themare occupied by the glove-fingers of the other baleen whales. The specimens for the histological preparation are obtained in the rectangular
block of about 5 x 5 x 10 mm from the curved extremity of the glove:finger, partially from its lateral side. These blocks are embedded in
the celloidin solutions and sectioned in the thickness of 10 µ after theinterval from two to three months, and followed by haematoxylin eosin,
Heidenhain's iron haematoxylin and AZAN staining. In relation to theformation of ear plug, the epitherial and connective tissues of the glovefinger are studies for the present problem.
The epidermis covering the most outward part of the glove-finger isthe stratified flattened epithelium, which the germinal and horny layer
constitute. The germinal layer is composed of the many cells in which
the basal cylindrical cell layer shows especially the aspect of progressive
cell division. Between the germinal layer and the hbrny layer there
are not the confirmatory aspects of the granular layer or clear layer
as seen usually in the thick epidermis. In the corium below the epidermis, there are characteristically many papillary layers, of whichshapes effect on the shapes of the laminae seen in the ear plug. The
sectioned specimen, Plate II, Fig. 2, suggests the collagen :fibers occupy
the most part of the connective tissue and the elastic fibers exist between them. The papillary layer project many papillae into the epidermis and the projection is remarkably in the papillae of the blue
whale. Plate I, Fig. l, shows the papillae of the blue whale and the different types of those of the fin whale. The papillae are about 5 mm solong in the projected extremity in the blue whale.• that they can be observed macroscopically. These papillae are not arranged regularly and it
is observed microscopically that there are many small papillae both twolarge papillae. In the corium of the blue whale the small papillae
characteristically distribute irregularly and they show the something
like a hive in the section as seen in Plate III, Fig. 2. This suggests
the intervening papillae are laterally pressed so intensively between two

124

T. ICHIHARA

developed long papillae that they form the curious constructure as if
the basal layer of the germinal layer subsides deeply into the corium.
In a papilla and below the papillary layer, there are many bloodvessels composed of blood capillaries, arterioles and venules. Although
the contents of the capillaries are often disolved out in the section,
they are sometimes occupied by the red blood corpuscles as shown in
Plate III, Figs. 1 & 2 and Plate IV, Fig. 1 in which the distal endof papilla of the blue whale and the papillary layer of the fin whale
are indicated. Any excretory ducts opening on the surface of epidermis
are observed nowhere in the specimens examined in which the cavities
exist a little apart from the basal layer of germinal layer. I disagreewith the presence of the ceruminous glands in the glove-finger, for thereason which Purves (1955) has interpreted. In Plate XVII, Fig. 3 ofhis paper, the abundant blood-capillaries are indicated as the ceruminous
glands, however, that section shows the presence of erythrocytes in thecavities which the endotherial cells surround, even if it is obtain fromthe old specimen.
With relation to the formation of laminae seen in the core of ear
plug, the shapes of papillae should be noticed. The structures likebands are divided into three parts macroscopically. One of them is thelight yellowish band arranged as fairly regular structures of concentric
circles from the proximal to the distal end of core, and the band of thesimilar light yellowish colour runs longitudinally in the core. Lastly
it is be noted that the dark coloured band exists between two light
concentric circles. These light concentric and longitudinal bands arestained well by SUDAN III and looks the yellowish red or red colours in thesections. In the microscopically examination, the macroscopical concentric light bands are really curved along the shapes of the projectedpapillae. With regard to this finding Plate V, Figs. 1 & 2 are referredin which the proximal part of core of the blue whale and fin whale
plug are indicated. Especially in the proximal end of the blue whale
specimen, a part of germinal layer remains and enables us to know
relation between the shapes of papillae and those of the light curved
bands. Since the papillae project irregularly into the ear plug and alarge papilla sometimes is more protrudent than another small papilla,
the lamination numbers are different from one column of tissue to anotherwithin the constant range from the outside curvature of glove-finger.
Here, the colume of tissue is defined as the tissue between two longitudidal light bands in the plug core.
In this connection, the lamination counting must be noticed particularly in the ear plug with the remarkably projected papillae in its glovefinger. It is furthermore desirable that the laminations are counted

EAR PLUG IN BALEEN WHALES

125

along the one longitudinal light band which is present in the middle
part of core. On the contrary the light curved bands become to distribute concentrically in the ear plug without so much projected papillae
in its glove-finger. It has been stated previously about a half of the
glove-finger of the fin whale has no markedly protrudent papillae andso its surface is fairly smooth.
The germinal layer of the epidermis of glove-finger remains usuallyin the most proximal end of the ear plug collected. Since the germinal
layer covers the papillary layer of corium, the most proximal end of
the ear plug collected sinks corresponding in position which the papillae
project. It is of interest to note that Malpighi's Ret is apparently
present there.
In the course of the study on the mechanism of ear plug formation, thehistological examinations are practised in the next two parts of core;
the first part of them concerns the curved light yellow band and thedark band between two light yellow bands. These bands are important
for the age determination of the baleen whale. The second part involves
the longitudinal light yellow band.
Concentrically curved light and dark bands. Specimens preserved in
10% formalin solution shortly after they are collected from the whale
body are partially embedded in the celloidin solutions, however, mostof them are prepared in the effectual frozen section since the paraffin
embedding is not available for such a deposited material as the ear plug.
Numerous specimens sectioned in thickness from 10 to 15 µ are stainedby haematoxylin eosin and SUDAN III.
Before the sectioned materials are produced, I measured the distance
between two curved light yellowish bands under a dissecting microscope.
N extly, the ear plugs of the frozen section were observed under the
dissecting microscope to measure the distance between two light bands.
After these preliminary processes, the position of the light band were
presumed from the distance between two bands in the section stained
by SUDAN III. Although the various fatty substances are observed to
distribute in the whole area of the stained section, the curved lightyellow band is confirmed as the parts stained darkly by SUDAN Ill.
These shapes of darkly stained bands, of course, are different from one
species to another, corresponding to the shapes of laminae. The stained
sections are shown in Plate V, Figs. 1 & 2. The curved dark band
between the two light yellowish bands is not stained well by SUDAN III
but by eosin. In the course of the examination on the numerous sections
from the proximal end of well fixed ear plugs, it has been fortunate
the light band and dark band are found under the formation, and it
facilitates to explain the process of formation,

126

T. ICHIHARA

In the stratified flattened epithelium, the cells of germinal layer are

generally elevated outerwards according to the increasing numbers ofcells in the basal layer. The epidermis of glove-finger belong to the same
categoly, however, the cells of germinal layer characteristically remain thedegenerated forms in the ear plug throughout the life span of whale.
Plate VI, Figs. 1 & 2 indicate the various transforming cells of thegerminal layer according to their distances from the basal layer. These
two photomicrographs are obtained from the fin whale plug sticking
to the outer surface of glove-finger. Plate VI, Fig. 2 shows the various kinds of cell forms near the basal layer and Plate VI, Fig. 1 indicates the transformation of cell in the more distal part. It is indicatedin this plate that the size of cell becomes not only larger and larger but
also its shape is deformed by and by soon after it is apart from thebasal layer. Lastly, it is flattened and becomes a fusiform cell of whichcytoplasm is stained well by eosin. Since the primitive stage of keratinized epithelium appears in these two figures, it must be illustrated subsequently how to already keratinized epithelium is deposited in the coreof ear plug. In Plate VII, Fig. 1 and enlarged Plate VII, Fig. 2, there
are many layers of accumulated keratinized epithelium. The fusiform
cells are destroyed in response to the passing of time, therefore, they
disappear in the distal end of the section from the old whale, forming
the developed kera tinized uniform tissue stained by eosin. The germinal
layer of epidermis of glove-finger remains in the lower parts of these
two figures and many nuclei are stained by haematoxylin.
It may be, therefore, safely said that the appearance of fusiform
cell corresponds to the beginning of conification, that is, to the first stageof the formation of curved dark band in the ear plug. In the courseof the keratinized degeneration of the germinal cell of glove-finger, thenuclei are deformed in the various stages. The deformation of nuclei
appear even in the cells near the basal layer of epidermis and the formsof nuclei vary greatly from one cell to another, for example, from theellipse to the circle, indicating sometimes the curious projection andnotch, as shown in Plate IV, Fig. 2 and Plate VI. The complicatedforms of nuclei may suggest the degenerated epithelial cells function
abnormally. These nuclei disappear soon after the fusiform cells occur.
Another case in which the light yellowish band is occurring is different greatly from the case of forming dark band mentioned above.
From the frozen section from other specimens of fin whale, I can obtain
the Plate VIII, Figs. 1 & 2, one of which is enlarged from the otherfigure to facilitate the explanation. The germinal layer in epidermis ofglove-finger remains in the lower part of Plate VIII, Fig. 1, besides
the band stained darkly by SUDAN III appears in the middle and theEAR PLUG IN BALEEN WHALES

127

keratinized fusiform cells are present in the upper part. This figure
indicates the light yellowish band has been just formed. In this connection see the enlarged photomicrograph, Plate VIII, Fig. 2 in which
the fatty degeneration of the cells in the germinal layer is illustrated.
In the first stage the fatty granules begin to appear sporadically inthe cystplasms of degenerated cells and they occupy the most part ofthe cystplasm in the second stage when the nuclei remain yet in thecompressed deformation. In the last stage, the fatty granules flow out
destroying the cell of developed degeneration and they forms the band
filled with the various fatty substances. The nuclei remain in the laststage as compressed forms among the fatty substances and stained byhaematoxylin, however, they disappear after all. In this connection it
is interesting to draw attention the sebaceous gland in which the degenerated cells filled with the fatty substances send out simultaneously
the involving fatty substance when they are destroyed. If the presenceof the gland must be stated persistently in the glove-finger, such glands
do not belong to the category of the eccrine and apocrine gland but tothat of the holocrine gland. As far as the fatty degeneration concerns,
the epithelial cells function rather like sebaceous glands. When thedark band is formed, the keratinized epithelial cells show the shapes
like the fairly obese fusiforms, however, in the case of the fatty degeneration they form usually the shapes of a little obese rounds. In
the latter case the deformed nuclei remain even when the cells filledwith fatty substances are destroyed at last. These differences muse beemphasized P2-rticularly in respect that the epithelial cells of glovefinger result so alternately in the fatty and the keratinized degenerationthat the light yellowish band and the dark band appear macroscopicallyin the regular concentric circles in the plug core.
In Plate VII, the fatty substances are observed to encircle the keratinized fusiform cells. This is explained from the next two findings.
Firstly in the course of keratinized degeneration, most of all epithelial
cells grow into fusiforms and they are stained well by eosin, however,a few of them remains rather roundly degenerated cells and the fatty
substances appear in their cystplasms. Secondly, into some parts of thelayer of keratinized epithelium, especially into the neighbouring parts
to the longitudinal light band, the fatty substances flow from the longitudinal light band through spaces of stratified fusiform cells. The
structure of the encircling fatty substances is compared to the sewing
the pieces of keratinized fusiforms cells together with the fatty substances and it may not keep the ear plug a very fragile material. The
keratinized fusiform cells appear sometimes in few frequencies in the

128

T. ICHIHARA

course of the fatty degenerations. The intervention of these substancesof different character brings forth the difficulity in case of the lamination counting. Abnormal ear plug showing coarse and fine laminations
which is indicated in Plate 6 by Purves & Mountford (1959) seems to be
an example of such a case. With regard to the second findings mentioned above, the longitudinal light bands are described in the nextpart.
Longitudinal light band. The longitudinal bands are observed as thelight yellowish structure homologous to the concentric light band in all
ear plugs from the various baleen whales and their positions are illustrated in Plates V & IX. It is noticed that the projections of papillae

LB

/

-

I

Fig. 9. Diagram showing the relationship between the arrangements ofnuclei and the direction of pressure from the basal layer of epidermisof glove-finger. Arrows indicate the direction of pressure. LB: longitudinal band, CB: concentric band, FC: fusiform cell, P: papilla. ·of glove-finger exist between two longitudinal light bands and the protrudent shapes of papillae bear closely on the formations of these bands.
The longitudinal yellow bands are stained by SUDAN III and shows
homologous structure to the curved light bands composed of various
fatty substances. The proximal end of ear plug is sectioned and stained
by SUDAN Ill, which is illustrated in Plate IX, Fig. 1 in this connection. It should be noted firstly the shapes of degenerated cell is different from those of the other bands.
The cells are so elongated in the longitudinal direction that the extremely proximal end of the longitudinal band looks like fine roots oftree. In the sectioned materials stained by SUDAN III, the orange
colour of the structure like fine roots is more apparent against the violet
colour of the nuclei of the germinal cell stained by haemotoxylin. The

EAR PLUG IN BALEEN WHALES

129

fatty degeneration of epithelial cell in the longitudinal band begin in
the earlier stage than the curved light band. In the longitudinal band,the compressed nuclei, their shapes corresponding to the elongatedepithelial cell, remain in the fatty substances which flow from the destroyed cells. It is endorsed by Plate IX, Fig. 2 of the section fromthe young plug that the nuclei remain for the long period in the plugcore. In this section stained by haemotoxylin and eosin, the papillaeof glove-finger are not so projected and it is shown in the lower partof that figure, however, the nuclei are not absorbed and remain in thelongitudinal band. Here it is pointed out that there is the similarityof fatty degeneration between the curved and longitudinal light band,

CB

LB

LB

Fig. 10. Diagrams showing the relation between the direction of the curvature in longitudinal light band and that in concentric light band. LB:
longitudinal light band, CB: concentric light band.

that is, the sizes of epithelial cells are not so enlarged in the fatty
degeneration as in the keratinized degeneration, and the deformed nuclei
appear in the cells filled with the fatty substances and remain yet longer
after the cell destroyed.
It is assumable that there is a close interrelationship among the deformed shapes of nuclei, the form of their arrangements and the directions of pressures dependent on the shapes of papillae. The photomicrograph is given in Plate IV, Fig. 2 to explain this relationship.
This photomicrograph is taken from the section with the projectedpapillae and so enlarged in the germinal layer between two large papillaethat the extremely proximal end of longitudinal band are surveyed. The
nuclei begin to be deformed in any part of the germinal layer soonafter the cells are apart from the basal layer. Characteristically between two large papillae, the nuclei are much flattened than the otherpart of germinal layer. This suggests the cells are flattened similarly

130

T. ICHIHARA

there. In the other part of the germinal layer the nuclei are arranged
along the curvatures of projected papillae. From Fig. 9 showing therelation between the arrangements of nuclei and the directions of pressure, the reason which the cells and nuclei are compressed laterally inthe longitudinal band is illustrated. The diagram indicates furthermore
the projection of papilla is effective on the formation of longitudinalband and on the shape of lamina formed upon it.
The longitudinal bands seem to run spirally from the proximal end to
the distal end of the plug core. It may be explained, however, from
Fig. 9 that there is no close relation between the longitudinal bandand the curved light yellowish band. Numerous frozen sections do notsuggest me that the curved light yellowish band is in general derived
from the longitudinal band as Purves (1955) has pointed out. He hasstated the structure like the longitudinal light band corresponds to theceruminous duct and the lipoids are secreted from the ceruminous glandin the corium of glove-finger in the resting period and the active formation of the squamous epithelium is seen in other period. If thecurved light band dues to the lipoid secretion from the ceruminous
gland of glove-finger, the left diagram in Fig. 10 always should be applied to the formation process of ear plug, however, there are various
relationships between the direction of the longitudinal band and that ofthe· curved light band and the right diagram in Fig. 10 is often applied.
Furthermore I can not observe always the second lamina is formed reversely in its curvature to the first lamina, on the contrary, the second
lamina curves similarly to the first lamina in the most of examined
specimens.
Based on the reasons referred above, I disagree with Purves' interpretation on the formation mechanism of ear plug. Yamada (1953) has
suggested the plug of ear wax seems to be produced by the meatal
epithelial and not the products of glands, however, he has not referred tothe core part of ear wax of Mysticeti. It was endorsed before in this paperthat the alternation of the dark and light band considered as the valid index of the age determination appears in the process of degeneration of theepithelial cells in glove-finger. Assuming the rhythmic growth in thepassage of time, I would like to conclude that such a degeneration ispracticed in response to many factors related to the metabolism of whale
body. Particularly the effect of hormone and enzyme on the metabolism
are regarded initially, and with the intractable problem of the inherent
physiological rhythm set aside, the external environment may effect onsuch a periodicity. On this subject further research remains a fascina ting one.
The incidental statements in the histological study are as follows.

EAR PLUG IN BALEEN WHALES131

The granules stained darkly by haematoxylin appear often in the longitudinal section of ear plug, and distribute irregularly in the degenerated
tissue. In the young specimens they appear more often than in theold specimens. Their abundance in the distal end of core characteristically may indicate the metabolism of the whale body in the very young
stage. It is, furthermore, of interest to note that many capillary crystals, not stained by SUDAN III, are observed in the formalin preserved
specimens. They distribute frequently in the longitudinal light andconcentric light band but sometimes in the layer of keratinized epithelium, concentric dark band. These crystals are indicated in Plate VIII,
Fig. 1.
SUMMARY

Glove-fingers and ear plugs from baleen whales were studied morphologically and histologically. The examined numerous specimens consistof 6 species, the blue, fin, humpback, sei, Bryde's and minke whale,
being collected from the Antarctic Ocean, the northern part of theNorth Pacific and from the adjacent waters to Japan from 1956 to 1959.
My findings are summarized as follows.
1. The size of glove-finger is constant throughout the life of whale.
2. The size of glove-finger varies from one species to another and it
gives a clue on the study of subpopulations located in the various areas.
In the northern hemisphere, the glove-finger of fin whale from theEast China Sea is significantly smaller in size than that from the northern part of the North Pacific.
3. The glove-finger are divided into three types from the shape of
papillae, which is effective on the shape of laminae seen in the core ofear plug. The papillae of glove-finger from the blue whale are protrudent remarkably from the outer surface of glove-finger. Moderately
projected and macroscopically not projected papillae occur in the glovefingers of fin and humpback whale. Papillae seem to be protrudent
litte by little at the increasing age of whale.
4. The core of ear plug seems to be formed in the prenatal stage ofthe baleen whales.
5. In the longitudinally bisected specimen, the breadth of plug coregrows in its the proximal end at the increasing age of whale. This finding
suggests the plug core is formed from the lateral side of glove-finger
in the old whale. The increases of breadth and length of core gives
the ear plug the conical form. The similarity in the size of core isrecognized in the two sexes.
6. There is no ceruminous gland in the corium of glove-finger. The

132

T. ICHIHARA

numerous small cavities observed in the corium are the blood capillaries.
7. The concentrically curved light band and longitudinal light band in
the plug core are composed of the various fatty substances. The keratinized epithelium of glove-finger constitutes the most part of the darkband between two curved light bands. These bands are derived fromthe degeneration of epithelial cells of glove-finger. In particular theperiodical occurrence of the fatty and the keratinized degeneration gives
the ear plug the validity of age determination.
8. It is not able to emphasize there is a close relationship between
the length of plug core and the lateral growth of skull. Based on thehistological examination the increasing length of core is rather dependent
on the internal progressing metabolism of the whale body. Since the alternation of light and dark band appear rhythmically in the plug core,
the effects of hormone and enzyme on the degenerations of epithelial
cells of glove-finger are regarded initially. Besides, the effect of theexternal environmental factors are presumed indirectly. Further studies
are needed on this subject.

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SCHIEFFERDECKER, P. (1922). Hautdriisen des Menschen und der Siiugetiere, ihre biologische und rassenanatomische Bedeutung, sowie die Muscularis sexualis, Stuttgart. 154p,
SEKI, M. (1954). [Histology]. Tokyo, Kyorinshoin, 351 p. (In Japanese).
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Hvalfangst-Tid., nr. 1: 37-45.
SYMONS, H. W. & WESTON, R. D. (1958). Studies on the humpback whale (Megaptera
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Rep. Whales Res. Inst., no. 8: 1-79.

EXPLANATION OF PLATESPLATE I
Fig. 1. Glove-fingers of the various baleen whales with indicating the three types of glovefinger from the fin whale ( x 1/2).
Upper: Fin whale, left to right; papillae are not projected, papillae are projected alittle, papillae are projected markedly, papillae are projected at the one side on
the _curved extremity of glove-finger.
Lower: Left to right; minke whale, Bryde's whale, sei whale and blue whale.
Fig. 2. Bisected ear plugs of the various baleen whales with the scale in cm.
Left to right: minke whale, 9 laminations; sei whale, 40 laminations; humpback whale,

134

T. ICHIHARA
24 laminations; fin whale, 29 laminations; blue whale, 41 laminations.
PLATE II

Fig. 1. Bisected abnormal ear plugs of the fin whale with the scale in cm.
Black substances interrupt the regular occurrence of laminae.
Fig. 2. Longitudinal sections of the curved extremity of glove-finger, from the baleen
whales, staining by haematoxylin eosin.
Left: Glove-finger of the fin whale ( x 15).
Right: Glove-finger of the blue whale ( x 7).
P: papilla, EP: ear plug, CT: connective tissue.
PLATE III
Fig. 1. Longitudinal section of the distal end of one papilla ( x 100), from the glove-fingerof blue whale, staining by haematoxylin eosin. This photomicrograph indicates theear plug is formed from the distal end of papilla and red corpuscles exist in the blood
capillaries of the corium.
GL: germinal layer of epidermis, BC: blood capillary.
Fig. 2. Longitudinal section of the many small papillae which are present between the
two large papillae ( x 100), from the glove-finger of blue whale, staining by haematoxylin eosin. This photomicrograph shows that the sectioned small papillae form thestructure like a hive and that there are the blood capillaries in corium.
LP: the proximal end of large papilla, SP: small papilla, BC: blood corpuscles.
PLATE IV
Fig. 1. Longitudinal section near the basal layer of epidermis ( x 100), from the glovefinger of fin whale, staining by haematoxylin eosin. In this section, the proximal endof ear plug sticks on the glove-finger. There are the blood capillaries in the corium.
EP: ear plug, BL: basal layer of epidermis, C: corium of glove-finger, V: venules.
Fig. 2. Longitudinal section of germinal layer of epidermis ( x 400), from the glove-finger
of fin whale, staining by haematoxylin eosin. This photomicrograph indicates theoccurrence of flattened nuclei in the proximal part of longitudinal band.
LB: the space corresponding to the longitudinal band, FN: flattened nuclei, BL: basal
layer of epidermis of glove-finger.
PLATE V
Fig. 1. Longitudinal section of the proximal part of ear plug ( x 20), from the fin whale,
staining by SUDAN III. In this photomicrograph the concentric light band and thelongitudinal light band are stained darkly by SUDAN III.
CLB: concentric light band, LLB: longitudinal light band, GL: germinal layer of glovefinger.
Fig. 2. Longitudinal section of the proximal part of ear plug ( x 15), from the blue whale,
staining by SUDAN III. This photomicrograph indicates the shape of curved light band
resembles to that of papilla.
CLB: curved light band, LLC: longitudinal light band, GL: germinal layer of glovefinger.
PLATE VI
Fig. 1. Longitudinal section of the extremely proximal end of ear plug ( x 400), from theear plug of fin whale, staining by haematoxylin eosin.
Fig. 2. Longitudinal section of the germinal layer near the basal layer of glove-finger( x 400), from the glove-finger of fin whale, staining by haematoxylin eosin.

EAR PLUG IN BALEEN WHALES

135

These photomicrographs are obtained from the same specimen. They indicate thevarious stages in the deformations of epithelial cells and nuclei, corresponding to the
distance from the basal layer of epidermis of the glove-finger. The conification ofepithelial cell progresses further and it is stained more darkly by eosin in the upper
part of Fig. 1 than in Fig. 2.
FC: fusiform cell, DEC: deforme depithelial cell, BL: basal layer of epidermis of glovefinger.
PLATE VII
Fig. 1. Longitudinal section of the proximal end of ear plug ( x 75), from the fin whale,
staining by SUDAN III. The specimen is forming the concentric dark band which is
not stained very by SUDAN III. The fusiform cells appear above the germinal layer ofglove-finger.
Fig. 2. Longitudinal section of the proximal part in which the keratinized fusiform cells
begin to be formed. ( x 400), from the same specimen as indicated in Fig. 1, staining
by SUDAN III.
FS: fatty substances occupying the space among the fusiform cells, FC: keratinizedfusiform cell, GL: cell of germinal layer under deformation.
PLATE VIII
Fig. 1. Longitudinal sectio~ of the proximal end of ear plug ( x 75), from the fin whale,
staining by SUDAN III. The specimen is forming the concentric light band which isstained well by SUDAN III. The keratinized fusiform cell appear above the partstained darkly.
FC: keratinized fusiform cell, CC: capillary crystal, GL: germinal layer of the epidermisof glove-finger.
Fig. 2. Longitudinal section of the proximal part of ear plug, in which the fatty degeneration in the epithelial cell of glove-finger begin to occur ( x 400), from the same specimen as indicated in Fig. 1, staining by SUDAN III. The fatty granules are stained in
the cystoplasm of the deformed cell.
PLATE IX
Fig. 1. Longitudinal section of the proximal end of ear plug ( x 200), from the fin whale
staining by SUDAN III. This photomicrograph indicates that the proximal part ofthe longitudinal light band forms the structure like the fine roots of the tree. The
germinal cells are compressed laterally in the longitudinal light band, which is stained
darkly.
LLB: longitudinal light band, GL: cell of germinal layer under deformation, P: thespace at which the papilla is situated.
Fig. 2. Longitudinal section of the ear plug and glove-finger ( x 40), from the young fin
whale, staining by haematoxylin eosin. Nuclei remain at the longitudinal light bandin the ear plug.
LLB: longitudinal light band, G: granules stained darkly by haematoxylin, CG: coriumof glove-finger.

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