Studies on the Pleuropodia of Embioptera,
Thysanoptera and Mecoptera
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Ando Hiroshi, Haga Kazuo
菅平高原生物実験所研究報告61‑81974
http://hdl.handle.net/2241/117141

Studies on the Pleuropodia of En1bioptera,
Thysanoptera and Mecoptera *by
Hiroshi ANDO and Kazuo HAGAPREFACE
Since the close of the last century, the pleuropodia of various insect orders havebeen studied by many investigators.

At present, therefore, there is a considerable

amount of knmvledge concerning the pleuropodia of embryo insects.

So far as theauthors are a\vare, however,pleuropodia

Mecoptera, and a few

there are nopapers

regardingtheofpapers concerning those of Embioptera and Thysanoptera(MELANDER, 1903; STEFANI, 1961; BOURNIER, 1966).
This paper deals with the development of the pleuropodia of the abovementionedorders, but does not deal \vith the functions of the pleuropodia.
The senior author wishes to express his thanks to Dr. Akira N!\G!\TOMI and Dr.
lunichi YUKA\VA of Kagoshima University and Mr. Akira MIYATA of Nagasaki University for their kind assistance in the present study.

MATERIALS AND METHODSAs materials the following species were used: OLigotoma jaj)onica OKAJlMA as Embioptera, Bactridothrzj)s brevitubus TAKAHASHI as Thysanoptera, Panorj)a j)ryeri MACHLACHLAN and Bittacus mastriLL££ N AV AS as Mecoptera.
Kagoshima City, B. brevitubus was captured at Mino-o0. jaj)onica was collected
111

111

Osaka Prefecture, and P.

j)ryeri and Bi. mastriLLii were caught at Sugadaira Plateau 111 Nagano Prefecture.

The eggs of these species were fixed in alcoholic Bouin's or Carnoy's fluid warmedto 60'-""70°C for 10.-...,30 minutes and they were cut into 6.-...,7 mIcra thicknesses andstained with Delafield's haematoxylin and eosin.

All drawings \\'ere made with theAbbe camera lucida.

OBSERV ATIONS
For the conveI1lence of description, the development of the embryos of O. jaj)onica
and B. brevitubus is divided into the following stages, viz., the early pre-revolution,
the middle pre-revolution, the late pre-revolution, the post-revolution, the late embryonic, and the full grown embryonic.
*Contributions from the Sugadaira Biological Laboratory of Tokyo Kyoiku University, No. 24SUGADAIRA

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No.6

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sdpalaatmdmxaIb

8Fig. 1 Embryos and pleuropodia of OLigotoma .la/Jonico
1. Embryo of early pre-revolution stage, 2. Embryo of late pre-revolution stage,
3. Embryo of post-revolution stage, 4. Pleuropodial anlage of early pre-revolution
stage (longitudinal section), 5. Pleuropodium of middle pre-revolution stage (long.
sec., 5'. cross sec.), 6. Pleuropodium of late pre-revolution stage (long. sec.),
7. Pleuropodium of post-revolution stage (long. sec.), 8. Degenerated pleuropodiumof late embryonic stage (long. sec.).
a : amnion, at: antennal rudiment, dp: degenerated pleuropodium, ec: ectodermal

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1.

ANDO & HAGA : Pleuropodia of Embioptera, Thysanoptera and Mecoptera

Embioptera:

3OL£gotoma jajx)nica OKAJIMA

Early pre-revolution stage:

The paired appendages develop on the ventral sideof the first to the fourth abdominal segments of the embryo.

They are of the same

shape and size as each other, but they are much smaller than the appendages or developing legs of the thoracic segments.

The pleuropodial anlage is found only at theapical part of the first abdominal appendages.

In longitudinal section it is seen thatthe anlage consists of several nuclei \vhich are larger than those of the ectodermal
cells forming the embryonic body vlall.

The size of the anlage is about: 20 X 10 micra(Figs. 1-1,-4).
2.

Middle pre-revolution stage:

In this stage, a conspicuous constriction appears

at the basal part of the pleuropodial anlage and consequently it is joined to the distal
part of the rudimental appendage of the first abdominal segment through the neckregIOn.

The anlage differs froni that of the preceding stage, that is, the nuclei in theanlage of this stage are arranged in a circle and the center of which is filled \\'ithcytoplasm.
3.

The anlage is about 20 X 15 micra in size (Figs. 1-2,-5).

Late pre-revolution stage:

A notable change has occurred111

the developing

pleuropodium, namely, it has grovvn to a distinct bulbiformed organ projecting fromthe appendage which is nO\\' smaller

111

size.

The pleuropodial cells themselves areespecially rich in cytoplasm and their boundaries are not very distinct.

They aregreatly elongated and become two or three times as tall as the neighbouring ectodermal cells.

The cytoplasmic basal part of the pleuropodium extends deeply into thebody wall and makes a thick root-like region (about 10 micra long) in \vhich may finefi brilate threads run parallel to each other from the proximal to the distal part of thepleuropodium.

A large nucleus containing remarkable chromatin granules

the outer end of each pleuropodial cell.
few vacuoles.

seen atIts cytoplasm is slightly stained and contains

In the present stage, the secretion of the pleuropodium has already be-gun in some cases.
4.

IS

The pleuropodium is about 25 X 18 micra in size (Fig. 1-6).

Post-revolution stage:

The structure of the pleuropodium is much the same asthat of the previous stage.

\Vhen the secretion begins, numerous granulated coagula-tions of the secreted substance appear at the circumference of the pleuropodium.

The

four paired abdominal appendages quickly degenerate after the katatrepsis or revolution of the embryo.
5.

The pleuropodium attains about 35 X 20 micra in size (Figs. 1-3,-7).

Late embryonic stage:

In this stage, the pleuropodium undergoes degeneration

similar to that observed in many other insects.

The abdominal appendages have al-

ready disappeared and the organ appears clearly atrophied.

Cytolysis is progressing

cells, 11, 1:): rudiments of 1st and 3rd thoracic legs, la: labral rudiment, lb: labialrud.,me: mesodermal cells,
md: mandibular rudiment,
mx: maxillary rud.,p: pleuropodium, pa: pleuropodial anlage, pd: proctodaeum, ps: pleuropodial
secretion, sd: stomodaeum

SUGADAIRA

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me~~--ee5me~r->&---4e cpppvne

pseFig. 2Embryos and pleuropodia of Bactr£dotimjx; brevitubus
1. 1st abdominal segment of middle pre-revolution stage (cross section), 2. Pleuropodium of middle pre-revolution stage (longitudinal sec.), 3. Pleuropodium of latepre-revolution stage (long. sec.), 4. 1st abdominal segment of embryo of postrevolution stage (cross sec.), 5. Pleuropodium of post-revolution stage (long. sec.),a : amnion, c: chorion, ec: ectodermal cells, I: rudimental thoracic legs, me:mesodermal cells,
p: pleuropodium,pc: pleuropodial cell,
pd: proctodaeum,
pp: protrusion of pleuropodial cell, ps: pleuropodial secretion, vnc: ventral nerve
cord, y: yolk

and rapidly advances towards dissolution, and at last no trace of the organ IS to befound in the embryo just before hatching (Fig. 1-8).
(2)
1.

Thysanoptera:

Bactridothrij)s brev£tubus TAKAHASI-Il

Middle pre-revolution stage:

In this stage the pleuropodium has grown to a dis-tinct globular organ, perfectly embedded in the embryonic body \vall as the pleuropodia of dragonflies (ANDO, 1953).

One is located on each side of the ventral nerve

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ANDO& HAGA : Pleuropodia of Embioptera, Thysanoptera, and Mecoptera

cord and opens into the amniotic cavity through an orifice (Figs. 2-1,-2).

5

In longitu-dinal section, the pleuropodium is composed of several large nuclei containing remarkable chromatin granules, and it is filled with cytoplasn"l similar to that observed in O.
jajJonica.

As yet there is still no sign of the cytoplasmic protrusions seen in the next

The developing pleuropodium is about 20 X 15 micra in size.

stage.
2.

Late pre-revolution stage:stage.

The pleuropodium attains full development 111 thisIn longitudinal section, the pleuropodial cells are very clear and become greatly

elongated and form the finger-like cytoplasmic protrusions projecting from the globularbody of the pleuropodium.
stage.

The boundaries of the cells are clearly seen in the present

The pleuropodium is about 40 micra long, about 30 micra wide, and the f111ger-like protrusion extending from the globular body of the pleuropodium is about 20-......-25
micra from the orifice and about 20--...,27 micra in width (Fig. 2-3).
3.

Post-revolution stage:

The embryo is undergoing dorsal closure.

The secretion

has occurred and the space between the ventral nerve cord and the inner margin of
the pleuropodium has increased, showing that the pleuropodium has moved towards
the pleural wall as the embryo 111creases 111 size.

The size of the pleuropodium isabout 25 X 30 micra (Figs. 2-4,-5).
4.

Full grown embryonic stage:

The pleuropodium has degenerated and disappeared

2Fig. 3laEmbryos of Pa71orl>a j)ryeri
1. Embryo of 90 hrs. after oviposition, 2. Embryo of 127 hrs. after oviposition.
abs 1 ,0: 1st and 6th abdominal segments, abss 4 : spiracle of 4th abdominal segment,
at: antennal rudiment, hi: head lobe, II, 3: rudiments of 1st & 3rd thoracic legs,
la: labral rud.,Ib: labial rud.,
md: mandibular rud.,mx: maxillary rud.,s: styliform appendage, y: yolk

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in the present stage.
(3)

Mecoptera:PanorjJC[ j)ryeri MACI-ILACHLAN and Bittacus mastriLLii NAVASIn the embryos of these species no pleuropodia develop in the embryonic life.
However, a pair of styliform appendages are formed in the each of the first to theeighth abdominal segments along the median ventral line of grown embryos (Figs. 31,-2).

DISCUSSION

1.

Embioptera.

MELANDEI< (1903) studied the structure and development of Embia texana (=OhgotOJnatexana (MELANDEI<)) and he briefly described the pleuropodia of this species as follows;"The pleuropodia are large, the remaining abdominal appendages are uniformly smallerand disappear on the fifth segment. (p. 115, Fig. 6)."appear before the embryo hatches.
bioptera.

According to him, they dis-This is the first record of the pleuropodia of Em-In 1914, KERSH Aw observed the embryonic development of Embia uhrichi,

but he did not mention the pleuropodia.

Recently STEFANI (1961) mentioned thepleuropodia of }-fajJloembia sohai as follows; "in questo precoce stadio embionale,degli abbozzi ben distinti di appendici (j)/euroj)odi di Wheeler) di forma e costituzione
simile a quelli toracici ma di mole ridotta.

Nallo stadio rappresentato dalla fig. 9 sono

gid com parse la primo q uattro paia. (pp. 13------14)."

The first and last statements seemto indicate the existence of the pleuropodia in the order Embioptera, but they containno histological studies of the pleuropodia.
As a result of the present study, it is clear that the embryo of O. jajxmica has apair of pleuropodia which are small bulbiformed organs projecting from the apical partof the first abdominal appendage.

Consequently it is doubtful that the "large or dis-tinct pleuropodia" observed by the two authors

referred to the first abdominal

appendage itself, and the present authors think that they may probably not be true
pleuropodia, especially in the embryo of O. texana.
The pleuropodia of O. jajxmica seem to be evaginated pleuropodia, but they differ
from the usual evaginated type, for instance those of OJ)istoj)/atia orientahs (ANDO, 1971).
The follovling are evident differences:

1. the pleuropodial anlage is formed by theconstriction of the apical part of the first abdominal appendage instead of the evagination from the ectoderm of the first abdominal segment; 2. no cavity is found in
the basal part of the pleuropodia.

II.

Thysanoptera
Since ULJANIN (1874) studied the embryonic development of Thrij)s j)hysajJUs, but

only by external observation, it is only natural that he did not notice the small pleuro-

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ANDO & HAGA : Pleuropodia of Embioptera, Thysanoptera and Mecoptera

podia of embryo thrips.

Recently BOURNIER (1966) studied the embryogenesis of Caudo-thrij)s bujfai and described the pleuropodia of this species.

As mentioned above, the embryo of B. brevitubus has a pair of well developed
pleuropodia classified as the invaginated type.

The development of pleuropodia of

this species and C. bujJai dosely resenibles those of heteropterous insects such as Saldal£ttoral£s (COBBEN, 1968) and others.

They also resemble those of Odonata (ANDO,1953), Lepidoptera and Coleoptera which have an invaginated type.
III.

MecopteraIn the middle stages of development, the embryos of P. jJryeri and 13i. J77astrilb havethe rudimental appendages except the abdominal segments.

In the latter stages ofdevelopment, however, the embryos have the developed cephalo-gnathal and thoracic
appendages and the paired styliform appendages in the first to the eighth abdominal
segments occurred along the ventral median line.

In these species belonging thefamilies Panorpidae and Bittacidae, the pleuropodia, \vhich are composed of glandular
cells, are not formed in the embryonic life.
Therefore the authors believe that no pleuropodia are found 111 these families of theorder Mecoptera.
IV.

Examination of the term "pleuropodia"

In 0. texana, 0. jajxJJ1ica and 1-!. solieri, the embryos

ll1

the pre-revolution stagesof development have four paired abdominal appendages 111 the first to the fourth abdominal segments.

MELANDER called the first appendages pleuropodia and also STEFANI

called all four paired appendages pleuropodia.

In 1890, \iVI-IEELER proposed the term

" pleuropodia" for the appendages of the first abdominal segment of the insect embryo.
He explained it as follows, "a name both suggestive of their origin from foot-likeorgans and their tendency, when fully developed, to take up a position on the pleuralwall of the embryo. (p. 87)."

In Embioptera, the pleuropodia and rudimental ab-

dominal appendages run into each other as mentioned above.

Accordingly it seems

that the definition given by \iVHEELER is obscure in the case of Embioptera.

Theauthors believe that one of the most important characteristics of pleuropodia is theirglandular nature, so that, even though a pair of the rudimental appendages are formedin the first abdominal segment, if they have no glandular nature, it may safely besaid that they are not true pleuropodia.

Therefore it is desirable that the definitionof pleuropodia must include the statement: "pleuropodia are glandular organs."

Anotherproblem occurs concerning the relationship between the pleuropodia and the prolegs
or abdominal appendages which are thought to show the polypod ism of the insect
embryos.

According to HINTON (1955) the prolegs are no true appendages in larval

insects, but this problem \:vill be discussed in future papers on the embryonic development of Mecoptera.

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SUMMARY
1.

2.

In this paper, the pleurapodia of Embioptera, Thysanoptera are described.
OLigotoma jaj)(mica of Embioptera has pleuropodia of a new type,externally re-sembling the evaginated type, and Bactridothrij)s brevitubus of Thysanoptera has
those of the invaginated type.

Panorj)a j)ryeri and Bittacus mastrillii of Mecoptera

have no pleuropodia.
3.

The secretion of the pleuropodia of O. jaj)onica and B. brevitubus occurs duringkatatrepsis

In

most cases, and the pleuropodia begin to degenerate shortly after

katatrepsis and disappear completely before hatching.
4.

The pleuropodia of Thysanoptera most closely resemble those of the heteropterousinsects.

5.

Some problems related to the character of pleuropodia are examined, and theterm pleuropodia is defined as the glandular appendages of the first abdominal
segment of the insect embryos.

LITERATURE CITED
ANDO, I-I. 1953.

Studies on the pleuropodia of Odonata.

Sci. Rep. Tokyo Bunrika

Daigaku, Sect. B. 7 (108): 167-----181.
ANDO, H. 1971.

Studies on the pleuropodia of an ovoviviparous cockroach, OJ)istoj)latia

orientaLis Burmeister (Blattaria : Epilampridae).

Bull. Sugadaira BioI. Lab. TokyoKyoiku Univ. (4) : 59-----71.
BOURNIER, A. 1966.

L'embryogenese de Caudothrij)s buJfai Karny (Thys. Tubulifera).

Ann. Soc. ent. Fr. (N.S.), 2 (2) : 415-435.
COBBEN, R. H. 1968.

Evolutionary trends in Heteroptera.

of the shell, gross embryology and eclosion.

Part 1. Eggs, architecture

Centre for Agr. Publishing &Documentation, Wageningen.
I-lINTON, H. E. 1955. On the structure, function and distribution of the prolegs of thePanorpoidea, with a criticism of the Berlese-lmms theory. Trans. R. ent. Soc.
Lond. 106. pt. 13: 455-----540.
KERSHAW, J. C. 1914.

Development of an Embiid.

Jour. R. Micr. Soc. 1914: 24--......27.

MELANDER, A. L. 1903. Notes on the structure and development of Embia texana(Mel.). BioI. Bull. 4 (3) : 99--......118.
STEFANI, R. 1961.

La formazione dei foglietti embrionali, l'origine dell'epitelio intesti-nale e la determinazione della linea germinale femminile nell' I-Iaj)Loenzbia soLieri.
Caryologia. 14 (1): 1--......30.
ULJANIN, W. N. 1874.

Observations on the development of thrips (Physapoda).

lzvia-stiia Imp. Ob. Liubit Estest. Anth. Ethnogr. 10: 39--"""43 (in Russian).
WHEELER, \lV. M. 1890.
insects.

On the appendages of the first abdominal segment of embryo

Trans. \lVisc. Acad. Sci. Arts & Letters. 8 : 87-----140.
(Sugadaira Biological Laboratory of Tokyo Kyoiku University)