A SECONDARY SEXUAL CHARACTER OF
THE SPERM WHALE
TOSHIO KASUYA AND SEIJI OHSUMIIn the Cetacea body length is commonly known as a secondary sexual character.
In the sperm whale the male grows larger than the female. The distance between
the center of genital aperture and anus shows also a sexual difference. Other
secondary sexual characters of the Cetacea are known on the shape of the snout of
the fin whale (Nemoto, 1962) and on the tooth of some Odontoceti.
A peculiar feature of the skin, a callus, on the tip of dorsal fin of the spermwhale was noticed in the summer season of 1964. We are convinced now that thisis one of the secondary sexual characters of the sperm whale, and report it here.
Many thanks are due to Dr. Keiji Nasu of the Whales Research Institute, whokindly collected the data and samples of the skin of dorsal fin. We are much indebted to Dr. Shyojiro Inoue of the Tokyo Medical and Dental University, who
discussed our materials and gave us valuable suggestions on endoclinology.
MATERIALS AND METHOD

Materials were obtained mainly from the whales captured in September and October
1964 and 1965 by the Japanese coastal whaling. In addition to them, 19 whales
captured in September 1965 under a special permission of the Japanese government for the scientific purposes and a female calf captured accidentally by a set
net were also used here.
The condition of the callus on the dorsal fin was recorded in the following three
categories, namely " present ", " absent " and " indistinct ". The " indistinct "includes the intermediate stage of the former two categories, where the conditionof skin on the top of dorsal fin is not quite smooth but shows a faint callus.
Together with this observation, mammary gland, number of corpora luteum
and corpora albicantia, weight of testes and fetus were observed, and the sexual condition of the animals was decided.
GENERAL CHARACTER OF THE CALLUS

The callus is found on the dorsal fin of most of adult females and some of young males.
It situates usually on the area around the top of dorsal fin, but in some animals
it situates on the anterior or posterior edge. The outline of the callus is nearlyoval or round, but it has a wide variation in size and shape. The shape and thesituation of the callus are shown in Text-Fig. 1 and PLATE 1, Figs. 1-3.
Differing from the smooth epidermis on the most parts of the body, the surfaceof the callus shows a roughness, which feature resembles to the surface of the small
89

, I'90

T. KASUY A AND S. OHSUMI

callosities of the right whale but the former is not so rough and hard as the latter.
The colour of the callus is paler than the other part of skin.
The vertical section of the callus is shown in PLATE I, Fig. 4. The depth ofepidermis of the callus is very irregular and is nearly I 7 mm at the thickest part and
5 mm at the thinnest part. The darmal papillae are more developed than thoseon the other part of skin but do not seem to differ much from the latter. Thebase of epidermis shows a wave form generally coinciding to that of the surface ofcallus, but the structure of the dermis and blubber does not show any difference
from that of the dorsal fin without callus. And so, we can not think that the callus
is a product of diseased skin.
RELATION TO AGE AND SEXUAL CHARACTERS
Table I shows the change of the frequency of the occurrence of callus in different
age classes. The age was determined by
the number of laminations in maxillary
tooth which are considered to be accumulated annually (Ohsumi et al., 1963).
In the males callus seems to occur
in some young animals, but entirely disappears in all males older than 9 years old.
The sexual maturity of the sperm whales isattained at the age of 9 or 10 laminations
in both sexes (Nishiwaki et al., 1958). The
age of the disappearance of callus in males
nearly coincides with the age at sexualmaturity. In the females, the occurrenceof the callus does not show clear relation
with the age of whales. However, callus
does not seem to appear in the calf.
The relation between the frequency
of callus and sexual conditions is shownin Table 2. In the males, maturity isclassified by the weight of larger testis,
namely the testes which weighs 0.4 kg orless is classified into immature, 0.5 kg0.9 kg into mature-I which is supposed toinclude the puberty, and 1.0 kg or more
into mature-2 respectively. In the females,
puberty includes those which have experi+--Anterior
enced ovulation but have no experienceFig. 1. Schematic figure of some variationsof pregnancy. The primiparous or mulin the position and size of callus (dottedtiparous was distinguished by the totalarea) on the dorsal fin of the sperm whale
number of ovulations and the state ofmam(lateral view.)

iI'

A SECONDARY SEXUAL CHARACTER OF THE SPERM WHALE

mary gland or whether it has experienced lactation or not.
females are not included in Table 2.

Male91

Some indistinguishable

TABLE 1.

FREQUENCY OCCURRENCE OF THE CALLUS IN AGE CLASSES

Ageabsent
indistinct
present0487

Female absent
indistinct
present29210224223111213414 15-24 25-34
9352

Total
23243I
3416735

22232174

OCCURRENCE OF CALLUS ON THE DORSAL FIN OF SPERM WHALE

TABLE 2.

Callus on the dorsal fin
SexTotal

Maturity

Maleabsent
591226

Immature
Mature-I
Mature-2
Total

indistinct
2present32410101232

781234248

6965576

4Female Immature
Puberty
Primiparous
Multiparous
Total73620Mature-I ; Larger tests weighs 0.5 kg-0.9 kg.
Mature-2 ; Larger tests weighs 1.0 kg or more.

Out of 22 mature males, the callus was observed only in one case which is a
newly matured male or in the stage of " mature-1 ". On the other hand, some of
the immature males have callus. Although the scarcity of immature samples does
not allow to conclude the frequency of the occurrence, the immature males withcallus seems not to be so rare. The callus observed in the immature period will
disappear after or near the attainment of sexual maturity, and probably the male
sex-hormone inhibits the manifestation of the callus.
TABLE 3.
Callusabsentindistinct
presentTotal

FREQUENCY OF CALLUS IN SEXUAL CONDITIONS OF
MATURE FEMALE
Resting3
37Pregnant
32
1116

Lactating222125

Lact. and preg.
145Total
953953Callus occurs on the female whales at every sexual conditions. Table 3 also
shows the frequency occurrence of the callus in various sexual conditions of mature
females. Fig. 2. is obtained from Tables 2 and 3, and it does not include 5 females

T. KASUYA AND S. OHSUMI

92

which are pregnant and lactating simultaneously. This figure shows that, in thefemales, the manifestation of callus begins in the immature. Its frequency increases in pregnant and lactating whales, and decreases again in resting whales.
There is an immature female with callus, which is suggested to attain soon thepuberty. And in the mature females, the formation of callus seems to have somerelations with the sexual cycle, although there is no evidence that the manifestation
or disappearance of callus is controled directly by some endoclinological factors.
When it is assumed, next supposition is possible. Chuzhakina ( 1961) concluded,
after histological observation, that corpus luteum tissue of the pregnant sperm whale
begins to degenerate when the fetal length attains to 199 cm. So the secretion of theprogesteron can be supposed to decrease in the latter half of the pregnancy as in thecase of some mammals. On the other hand, secretion of estrogen, though which is10075-~>-uc50Q)=>
CT"[ll250lmm.

Pub.

Pre g.
SexualLact.

Rest.

conditions

Fig. 2. Frequency occurrence of the callus in various sexual conditions in females.
Whales lactating and pregnant simultaneously are excluded. White: absent,
Dot: indistinct, Horizontal line: present.

not studied in the sperm whales, is known in many mammals to increase gradually
untill just before the parturition, and it is also secretted in the immature and mature
mammals of both sexes in various degree. As mentioned above, callus is found on
the immature animals in both sexes and on the mature females, so we prefer tothink that estrogen has charge of the manifestation of callus and that androgen
inhibits it.
We have rare chances to observe the dersal fin of 7 fetuses (3 males and 4females, body lengthes 51-108 cm) but callus was not found on them. And there
was no callus on the dorsal fin of a new born female calf of which body length was426 cm. We must get more materials on the fetal and calf stage of the sperm whale,
and it is one of the subject to investigate the age when the callus appears on the dorsalfin.
Callus on the dorsal fin in the sperm whale is different from callosities on themouth parts of the right whale, because in the latter whale they appear already infetal stage, and they are found in every one.

A SECONDARY SEXUAL CHARACTER OF THE SPERM WHALE

93

SUMMARY

A secondary sexual character of the sperm whale is reported based on the materials
obtained from the Japanese coastal waters.
1. A callus is formed on the skin near the top of the dorsal fin of some spermwhales.
2. The shape of callus is nearly round or oval, and it is distinguished externally from the usual skin by paler colour and unevenness. Internally, it ischaracterized by a well developed thick epidermis.
3. The callus is not observed on the fully mature males, but observed on someimmature one.
In the females, it occures more often on pregnant and lactating whales thanon the immature, pubertal and resting whales.
4. It is presumed that male sexual hormone inhibits the manifestation of thecallus, and some female sexual hormone, probably estrogen, stimulates it.
REFERENCESAsDELL, S. A. ( 1946). Patterns of mammalian reproduction. 437 p. Comstock Pub. Co., New York.
CHUZHAKINA, E. S. ( 1961). Morfologicheskaya kharakteristika yaichnikov samok Cachalota (Physeter catodon
L. 1758) v svyazis opredeleniem vozraska. Trudi Inst. Mor. ,(hivotnith A.N.S.S.S.R., 34: 33-55.
NEMOTO, T. (1962). A secondary sexual character of fin whales. Sci. Rep. Whales Res. Inst., 16: 29-34.
NISHIWAKI, M. & HrnIYA, T. (1951). On the sexual maturity of the sperm whale found in the adjacent watersof Japan (1). Sci. Rep. Whales Res. Inst., 6: 153-66.
N1sHIWAKI, M., Hrn1vA, T. & 0HSUMI, S. (1958). Age study of sperm whale based on reading of tooth laminations Sci. Rep. Whales Res. Inst. ibid., 13: 135-53.
N1sHIWAKI, M., 0HSUMI, S. & MAEDA, Y. (1963). Change of form in the sperm whale accompanied withgrowth. Sci. Rep. Whales Res. Inst., 17: 1-14.
0HSUMI, S., KAsUYA, T. & N1smwAKI, M. (1963). The accumulation rate of dentinal growth layers in themaxillary tooth of the sperm whale. Sci. Rep. Whales Res. Inst., 17: 15-35.
PARRY, D. A. (1949). The structure of whale blubber and a discussion of its thermal properties. Quart.
]our. Mier. Sic., 90: 13. (Cited by Slipper, 1962).
SLIJPER, E.J. (1962). Whales, 475p. Hutchinson Co. London.

94

T. KASUYA AND S. OHSUMIEXPLANANATION OF PLATE
Fig. 1.
Fig. 2.
Fig. 3.
Fig. 4.

Lateral view of dorsal fin without callus, adult male.
Lateral view of dorsal fin with callus, adult female.
Dorsal view of dorsal fin with callus, adult female.
Section of skin of the dorsal fin through callus, adult female.

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