the morphology of the thorax of telea polyphemus (lepidoptera). i. skeleton and muscles

T H E MORPHOLOGY O F T H E THORAX O F TELEA POLYPHEMUS (LEPIDOPTERA)

I. SKELETON AND MUSCLES

HANS NUESCH Zoological Institute, University of Basel, Switzerland

[Dedicated to Prof. F. Baltzer on occasion of his 70th anniversary, Harch 12, 19541

FIVE FIGURES

The extirpation of ganglia or the cutting of single nerves in the thorax of diapausing pupae of the American silkworm, l'eleu polyphemus, results in adult moths in which certain groups of muscles are lacking. This fact shows that the muscle anlagen of the pupa require innervation in order to develop normally during the formation of the adult moth (Nuesch, '52 ; Williams and Schneiderman, '52).

I n such experiments the detailed analysis of the effects of denervation necessitates a precise knowledge of the normal morphology of the thorax, particularly in view of the fact that certain muscles have been observed to develop after certain types of operation. The present paper provides a description of the thoracic muscles ; in another paper the structure of the nervous system will he considered.

Muscles cannot be studied without an accurate knowledge of the skeleton, for the reason that both skeleton and muscle represent a single functional unit. Therefore, I shall first provide a summary of the anatomical components of the skeleton which are used in the description of the muscles. A detailed study of the slreleton will also afford a foundation for subsequent investigations of a different character. I t still remains an open question whether muscle stresses during development influence the structure of the insect skeleton (Weber, '33; Malouf, ' 3 5 ) . I n the above mentioned extirpation experiments one markedly upsets the relations be-

589

590 HANS NUESCH

tween skeleton and muscles during the development of the adult moth; consequently one can judge how the skeleton develops in the absence of the muscles. As far as the ex- amination has already progressed, the skeleton appears to be essentially normal, even if all imaginal muscles are absent. Only minor differences have been encountered. The study of the normal skeleton will serve also as a basis for the interpretation of these abnormalities.

METHODS

The adults of TeZea polyphemus Cr. (Saturniidae, Lep.) were fixed in alcoholic Bouin's solution and dissected after being split sagittally. Small muscles, as well as parts of the large muscle masses, were also examined in serial sections. The skeleton was studied in specimens treated with 20% KOH solution.

Skeletovz

The general morphology of the insect thorax has been fully described by various authors, especially by Kerlese ( '09), Snodgrass ( '35) and Weber ( ' 33 ) . A comparison of the sliele- ton of T. polyphemus with the drawings given by those iii- vestigators often led to difficulties in homologizing certain parts. Therefore, the drawings here shown are intended only to give an accurate picture of the structure of the thorax of T. polyphemtns without entering into a discussion as to the problematic interpretation of the different parts.

Figure 1 is an internal view of the right half of the head and the thorax, viewed from the sagittal plane. It is schema- tized as little as possible. In order to facilitate the coin- parison of these structures with the data in the English and German literature, the accompanying table records the anatomical terms of the skeleton, particularly those applied in the description of the muscles by Snodgrass ('35) and Weber ( '28, '33). The terms recorded in parentheses are not used by these authors. The abbreviations appearing in table 1 are those applied in the present paper.

SKELETON AND MUSCLES O F TELEA 591

In the description of the Polyphemus thorax the termin- ology of Snodgrass has been followed as closely as possible.

Muscles The following list of the muscles in the thorax of Telea

polyphemus is the result of the dissection of many specimens. With a very few exceptions I always found the same arrange- ment (see below). Some muscles are so small that they had to be examined histologically to prove their muscular nature.

The principal difficulty encountered was the nomenclature of the muscles. The purely morphological system utilized by Weber ('28, '33) seems to me to be more suitable than those which also consider the function, as in the case of the nomenclature of Snodgrass ( '35) and Maki ( '38). Thus the main groups of muscles are : Dorsolongitudinal muscles (dl) extending between parts of the ter-

Ventrolongitudinal muscles (vl) extending between parts of the

Dorsoventral muscles (dv) arising on the tergum and inserting on

Pleurodorsal muscles (pd) extending between the pleurum and the

Plenroventral muscles (pv) extending between the pleurum and the

Pleural muscles (p ) extending between parts of the pleurum. Sternopedal muscles (st) arising on the sternum or the furca and

inserting on the leg. Coxal muscles (ex) arising on the coxa and inserting on the trochanter. Spiracular muscles (s) opening or closing the spiracle.

Wherever possible, the same abbreviation and subscript have been used for muscles with serial homology; i.e., with the same origin (with few exceptions such as IIpdzc) and the same insertion. If a muscle mass is subdivided into two or three fasciculi with like origin and insertion, these individual fasciculi are indicated by the letters a, b, etc. added to the subscript. Roman numerals (I, 11, 111) preceding the abbreviation indicate the thoracic segment.

gum.

sternum and its apophyses.

the sternum or the leg.

tergum or the wing base.

sternum or the leg.

592 HANS N ~ E S C H

TABLE 1

Anatomical terms of the lepidopterous thoracic skeleton

SNODGRASS WEBER ABBREVIA- TION

Tergum antecosta Antecosta phragma Phragma

prescutum Prascutum prealar bridge Tergalarm prescutal ridge Parapsidalleiste

anterior notal wing

(tergal fissure) Tergalspalt (median notal wing

posterior notal wing

(inner ridge) Innenleistr V-shaped notal ridge V-Leiste

scutelluin Scutellum axillary cord Flugelligament

postnotum Postnotum postalar bridge Lateropostnotum (process on the Postnotalhaken =

postalare) Laterophragma

scutum Scutum

process vorderer Tergalhebel

process) hinterer Tergalhebel

process hinterer Gelenkfortsatz

Pleurum episternum Episternum supraepisternum (episternal fissure) Episternalspalt iuf raepisternum prepectus =

prcepisternum + Praepisternit presternum Prasternit

(episternal ridge) (Episternalleiste) precoxal bridge pracoxale Briicke (ridge on the prepectus, Priiapodem

not homologous to episternal ridge)

to ‘ preapodema ’ ’) (narrow strip anterior Hypopteron

pleural ridge Pleuralleiste pleural wing process pleuraler Flugelgelenkkopf pleural apophysis Pleuralarm, Pleuralhaken tegular arm Tegulararm

postcoxal bridge postcoxale Briicke epimeron Epimerum

awp tf

PWP ir Vr sel

epsf

epsr

Plr plwp

SKELETON AND MUSCLES O F TELEA

TABLE I (continued)

SNODGRASS WEBEK.

Sternum

1

Coxa

Wing base

593

~~

ABBREVIA- TION

epipleurites basalare subalare

spiracle

spinasternum spina

eusternum presternum basisternum furcasternum median ridge of the

sternum furca furcal arms

basicoxite basicosta meron (sternoeoxale)

p teralia first axillary

second axillary third axillary fourth axillary

median plates tegula

Pleuralgelenkstiicke Basalare Subalare Stigma

Poststernit + Prasternit Spina

Prasternit, Basisternit Furcasternit

Sternalgrat Furca paarige F-ircaaste

Basicoxale + Meron Basicosta + Meroeosta Meron Sternocoxale

b a sa SP'

ss SP

f s t

mr f

be + me m stcx

Pteralia = Fliigelgelenkstiicke Pterale 1 = vorderes

Pterale 2 = Mittelgelenkstiick Pterale 3 = Analgelenkstiiclt Pterale 4 = hinteres

Verniittlungsplatte Tegula

Tergalgelenkstuck ax

Tergalgelenkstuck rxvp

The homologies of the muscles in the prothorax are much less clear than those in the pterothorax, as one might predict from the differences in the skeleton. As a standard of refer- ence I selected the muscles of the pterothorax. Those muscles in the prothorax which could not be homologized with single fasciculi in the mesothorax but which still belong to the same muscle group have been given the same abbreviation; the subscript number in this case has been replaced by a letter. The muscles moving the head and the neck could not be homologized with the muscles in the thorax. Therefore they

594 HANS NUESCH

are grouped into dorsal, ventral, tentorial and cervical muscles according to the point of insertion. Perhaps it will be possible to homologize some of these muscles with those of the pterothorax when we know more about their innervation and mode of the development. Up to now, it is completely unknown how the direction of a muscle anlage with its points of origin and insertion is determined.

In the description of the individual muscles, I have added the key numbers and abbreviations used by Snodgrass (S; '35, diagrammatic), Berlese ( B ; '09, Sphinx) and Weber (W; '28, Papilio) to facilitate comparisons with other Lepi- doptera. In the mcsothorax the terms used by Maki (11; '38) are also recorded. I t is beyond the scope of the present paper to compare in detail the muscles of Teleu polyphemus with those of other Lepidoptera. Some of the differences between the various species are evident in the annotations, and addi- tional information on this point is found in Maki's ('38) description of 5 Lepidoptera.

Head

There is no clear limit between the dorsal and ventral region of the head capsule. Therefore the distinction between dorsal and ventral muscles is only an arbitrary one. The muscles inserting on the postocciput above the base of the tentorial bridge where the cervicalia articulate, act as ele- vators of the head. Muscles inserting below this point act as depressors of the head. In describing the muscles I have selected the base of the tentorial bridge as an artificial limit between the dorsal and the ventral region of the head capsule. The muscles have been numbered according to their points of insertion on the postocciput, from dorsal to ventral.

dl Dolrsal muscles : (B : 140a) a thin muscle which arises on the ventral end of the prealar arm at the limit of pro- and mesothorax and inserts mediodorsally on the postocciput. (B : -) a broad thin muscle which arises on the anterior edge of the scutnml and inserts on the postocciput, lateral to dl.

da


(B : 140), a very thin muscle which arises laterally on the postnotum and inserts laterodorsally on the postocciput. (B : 147), a thick muscle arising on the anterior arm of the cervicale and inserting on the base of the postoccipital ridge in front of dz and d3. (B : CXXXIII) , a thick muscle which arises on the medial part of the prescutuml and inserts on the postocciput lateral to d3. (B : CXLI) , a thin muscle which arises on the dorsal edge of the furcal and inserts with a long tendon on the lateral corner of the postocciput.

V e n t r a l musc le : (13 : 137), a broad thick muscle which arises on the median edge of the furcal and inserts with a short tendon on the ventrolateral end of the postocciput.

M m c l e in ser t ing on t h e tentorial b r idge : (B : CXXXIV) , a thin tapering muscle. It arises on the anterior

edge of the episternum where the pleural ridge joins with it, and inserts medially on the tentorial briclge.

Muscles moving t h e a n t e n n a : Three muscles, of which the anterior is the largest,; they arise on an enlargement of the anterior arm of the tentorium and insert 011 the inner edge of the first joint of the antenna.

Neck

Two muscles extend between the cervicalia and the prothorax. Uncertainty regarding the serial homologies again requires the use of more general designations (cervical dorsal and cervical ventral). cd (B : -) , a very thin muscle which arises on the ventral end of

the prealar arm and inserts on the anterior end of the anterior arm of the cervicale. (B : 135), a flat thin muscle with parallel fibers arising on the median part of the furcal just in front of muscle v and inserting on the ventral arm of the cervicale.

cv

Pro t ho r n s

Because of the different morphology of the first thoracic segment in comparison with the meso- and metathorax, only certain of the muscles could be strictly homologized with cor-

596 HANS NUESCH

responding muscles in the pterothorax. Others will be desig- nated with the subscripts a, b, c.

Dorsolongitudinal muscles: (€3 : CIX) , a thin muscle arising medially on the prescutum and inserting on the postnotum next to the median line. (B : CXV), a thick muscle which arises laterally on the broad anterior plate of the scutum and inserts on the small tendon plate a t the end of the prealar arm.

Ventrolongi tudinal nzzcscles: (B : 105-106 ; W : Ivlnil), a thin muscle not clearly divided into two fasciculi. It arises on the posterior edge of the fareal and inserts partIy on the median anterior tendon of furca? and partly directly lateral to this tendon on the furcaz. (B : 108 ; W : Ivlmz), thicker than v11, somewhat bellied, arising laterally on the fLircal next t o vll and inserting with a short tendon on the apex of the spina.

Dorsoventral nzztscle: (B : 112) , a thick muscle arising on the lateral end of the furcal and inserting on the anterior side of the prealar arm. If one takes the edge of the phragma and the laterophragma as the limit between the pro- and the mesothorax, then the anterior side of the prealar arm belongs t o the prothorax and this muscle attached to it does not cross the segmental limit (Weber, '33: ism).

Pleurodorsal m u s c l e s :

(B : CXVl) , a thick muscle which arises on the sclerite behind the thickly chitinized anterior edge of the prescntuni and episternum and inserts on the base of the small traiisiTerse ridge behind the pleural ridge. (B : CXVII ? ) , a thin muscle which arises on the lateral anterior edge of the scatum with a short tendon and inserts behind pd, on the same small ridge. (B : -) , a thin muscle arising on the phragma of the postnotum and inserting on the pleural ridge just behind the connection with the anterior episternal ridge.

PlezwovPniral nzzcscles: (B: CXXIII ) , a thick muscle arising on the underside of the small transverse ridge behind the pleural ridge and inserting on the edge of the coya, on the laterocaudal side.

SKELETON AND MUSCLES OF TELEA 599

dvg ( S : J ; B : 75; W: dvms; M:tergal remotor of the coxa), somewhat less thick than dv4. It arises on the scutum, caudal to dv3, and inserts on the meron laterocaudal to dvq.

Pleuradorsal muscles : pdl (S : 2B ; B : 87 ; W : pm3 ; M : ordinary tergo-pleural) a short

thick muscle which arises on the prealare and inserts on the basalare above the tendon cap.

( S : D ; E : XCII+85 ; W : pm4 ; M : pleuro-axillary) a large muscle consisting of three separate fasciculi. Fasciculus a arises

pd23,b,C -

above the episternal fissure on the supraepisternum ; fasciculus b on the infraepisternum behind the episternal ridge ; fasciculus c on the epimeron caudal to the pleural ridge and above the latter’s knee. All three fasciculi insert on the medial edge of the dorsal third axillary sclerite. (S : - ; B : - ; W : pm;, ; AT : ordinary tergo-pleural) , a rather thin muscle arising on the pleural ridge above the articulation of the coxa and inserting on the anterior ventral edge of the first axillary sclerite. (S : 3B ? ; B : LXXVI ; W : - ; M : -) , a small flat muscle which arises on the anterior half of the tegular arm and inserts on the small sclerite medially above the attachment of the tegnlar arm on the scntal membrane. (S : -; B : XCI ; W : - ; M : ordinary tergo-pleural), a very thin muscle ivhich arises on the lateral edge of the scutum and inserts on the ventral edge of the basalar tendon cap, opposite to part of pv1.

Pleuroventral naacscles: (S : 1E’+2E’; E : 91+91a ; W : pml ; M : sterno-basalar), a very thick muscle tapering to its insertion. The muscle arises on the prepectus lateral to dvl ; a smaller part may also arise behind the episternal ridge. Most of the fibers insert on the anterior third of the basalar tendon cap ; a small anterior part inserts on the lower edge of the tendon cap a t the same point as pd5. (S : 3E’; B : 82 ; W : pma ; M : coxo-basalar), less thick than p1-1 with parallel fibers. The muscle arises on the basicosta lateral to dva aiid inserts on the middle and posterior third of the basalar tendon cap. (S : P ; B : 81 ; W : -; M : trochantero-basalar) a very thin muscle arising on the caudal edge of the basalar tendon cap and inserting together with dv3 on the median tendon of the trochanter.

598 HANS NUESCH

subdivided into 5 muscle masses which are more or less inde- pendent in their contraction in response to electrical stimulation. The lowermost fasciculus a arises on the first phragma, fasciculus b on the prescutum, and c, d, and e on the scutum; all 5 fasciculi insert on the second phragma and the postnotum. ( X : IA ; B : 71 ; W : dlm2 ; M : lateral dorsal), a thin muscle arising on the lateral scutum behind the dv5 muscle and inserting on the phragma-like process of the postalar bridge. I ts extension is parallel to the dorsoventral muscles. X, B, W : -; M : median dorsal) , a very thin flat muscle attached t o the pulsating organ in the scutellum. It arises on the V-shaped ridge and inserts on the anterior edge of the postnotum, almost medially.

Ventrolongi tudinal mziscles: (X : H ; B : 68 ; W : vlmli2 ; M : longitudinal ventral) , a strong muscle more or less clearly divided into two fasciculi. Both arise on and lateral to the tendon of the furcaz and insert on the lateral plate of the furca,. (S : H ; B : 104 ; W : -; M : mesospino-mesofurcal ventral), a very thin muscle which arises on the apex of the spina and inserts on the furcan. It lies lateral to Ivll and is without tendon.

Dorsoventral muscles: dvla+, ( S : C ; B : LXXVIII ; W : dvm, +2+5 ; M : anterior tergo-sternal) ,

two thick muscle masses separated by a layer of tracheae, each one dorsally subdivided into two parts by the inner ridge of the scutum ; ventrally each forms one single muscle mass. The muscle arises on the scutum, lateral to the longitudinal muscles, and medial and lateral to the inner ridge ; it inserts on the sternum alongside the median ridge and in front of the episternal ridge. (S : I ; B : 74 ; W : dvm,,, ; M : tergal promotor of the coxa), a thick muscle, dorsally subdivided into two equal parts by the inner ridge. It arises on the scutum, caudal to dvlb, and inserts on t,he median part of the basicosta. (X : P, 133c ; B : 76+77 ; W : dvm,,, ; M : tergal depressor of

the trochanter) , two thick well separated muscle masses arising on the scutnin caudal to dva; fasciculus a is medial, fasciculus b lateral to the inner ridge. Both insert on the median tendon of the trochanter. (S : J ; B : 75 ; W : dvms ; M : tergal remotor of the coxa) , a thick muscle which arises on the scutum, lateral to dv5 and caudal to dv,,. It inserts on the ventral corner of the meron immediately behind the merocosta.

dvz

dvla+b

dv4


dvj (S: J; B : 75; W : dvm8; If: tergal remotor of the coxa), somewhat less thick than dv4. It arises on the scutum, caudal to dv3, and inserts on the meron laterocaudal to dvq.

Pleztrodorsal muscles: pdl (S : 2E ; E : 87 ; W : pm3 ; M : ordinary tergo-pleural) a short

thick muscle which arises on the prealare and inserts on the basalare above the tendon cap.

( S : D ; E : SCII+85 ; W : pm4 ; M : pleuro-axillary) , a large muscle consisting of three separate fasciculi. Fasciculus a arises

pd23,b,C -

above the episternal fissure on the supraepisternurn ; fasciculus 7, on the infraepisternum behind the episternal ridge ; fasciculus c on the epimeron caudal to the pleural ridge and above the latter’s knee. All three fasciculi insert on the medial edge of the dorsal third axillary sclerite. (S : - ; B : - ; W : pm5 ; M : ordinary tergo-pleural) , a rather thin muscle arising on the pleural ridge above the articulation of the coxa and inserting on the anterior ventral edge of the first axillary sclerite. ( S : 3B ? ; B : LXXVT ; W : - ; M : -) , a small flat muscle which arises on the anterior half of the tegular arm and inserts on the small sclerite medially above the attachment of the tegular arm on the scutal membrane. (S : -; B : XCI ; M’. - ; M : ordinary tergo-pleural), a very thin muscle which arises on the lateral edge of the scutum and inserts on the rentral edge of the basalar tendon cap, opposite to part of pv1.

Pleuroventral vnztscles: (S : lE’+ZE’; B : 91+91a ; W : pml ; M : sterno-basalar) , a very thick muscle tapering to its insertion. The muscle arises on the prepectns lateral to dvl; a smaller part may also arise behind the episternal ridge. Most of the fibers insert on the anterior third of the basalar tendon cap ; a small anterior part inserts on the lower edge of the tendon cap at the same point as pdj. (S : 3E’; I3 : 82 ; W : pm2 ; &I : coxo-basalar) , less thick than pvl with parallel fibers. The muscle arises on the basicosta lateral to dv2 and inserts on the middle and posterior third of the basalar tendon cap. (S : P ; B : 81 ; W : - ; M : trochantero-basalar ) , a very thin muscle arising on the caudal edge of the basalar tendon cap and inserting together with dv3 on the median tendon of the trochanter.

600 HANS NUESCH

PV4

P1

P2

S t l

stz

stg

(S : 3E” ; B : 84 ; W : pm7 ; M : coxo-subalar) , a very thick muscle which arises on the meron lateral to dv4 and just behind the merocosta. It inserts on the subalar sclerite in front and lateral t,o the tendon cap. ( S : 3E” ; B : 84 ; W : pms ; M : coxa-subalar) , a very thick muscle arising on the meron lateral to dv5 and caudal to pv4 and inserting on the tendon cap of the subalare. (S : 2111 ; B : 83 ; W : pm6 ; N : pleural abductor of the coxa) , a flat and thin muscle, tapering to a tendon. It arises on the episternum just in front of the pleural ridge and inserts by a short tendon on the lateral end of the basicosta. (S : G ; B : 100 ; W : - ; M : furco-ent,oplenral) , a flat fan-like muscle arising on the pleural ridge between the knee and the coxal articulation and on the epimeron adjacent thereto. It passes between dv, and dv4+5 and inserts with a long tendon’ on the furcaz. ( S : - - , B : 73a ; W : - ; M : sterno-basalar) , a rat,her thin muscle which arises on the caudal tendon of the furcaz lateral to vll; i t crosses the segmental limit and inserts on the tendon cap of the basalare,.

Pleural muscles: ( S : 1E” ; B : CIV ; W : pm9 ; M : pleuro-subalar) , a short and thick muscle which arises on the dorsal part of the epimeron and the dorsal end of the furcaz. It inserts on the caudal side of the subalar tendon cap and also on the subalare sclerite. ( S , E, W : - ; M : possibly corresponding to the first tergo-pleural muscle in the metat,horax), a short thin muscle with interseg- mental extension. It arises by a short tendon on the dorsal end of the furcaz and inserts on the knob on the dorsal end of the pleural ridge,.

Sterrnopedal muscles: ( S : K ; B : 93; W : bml; M : ordinary sternal promotor of the coxa) , a flat muscle which arises on the caudal part of the median sternal ridge and on the ridge of the furcasternum, and inserts on the coxa, medial to the front of the st,erno-coxal articulation. ( S : P, 133; B:-; W : bmp; M : sternal depressor of the trochanter), a rather thick muscle which arises ventrally on the median tendon of the furcaz and inserts on the median tendon of the trochanter. (S : L ; B : - ; W : bm3 ; M : ordinary sternal remotor of the coxa) , a thin flat muscle which arises on the posterior side of the ridge on the furcasternum and inserts caudally on the dorsal edge of the meron.


( S , B, W : -; M : sternal remotor of the coxa?), a thin flat muscle arising ventrally on the base of the furcaa and inserting on the tendon of the merocosta.

Coxal muscles: ( S : Q , 133a ; B : -; W : cxm4) , a thick muscle which arises medially on the underside of the basicosta and inserts on the anterior side of the median t,endon of the trochanter. ( 8 : 0, 131+132; B:-; W:cxml) , a large flat muscle which arises laterally on the underside of the basicosta and on the inerocosta and inserts on the lateral tendon of the trochant,er. (S, B, W : -;) , a thin muscle arising on the ventral edge of the sternocoxale and inserting on the caudal edge of the trochanter.

Met at horns

For most of the muscles in the mesothorax there are serial homologues in the metathorax. The same abbreviation indi- cates origin and insertion on corresponding skeleton parts. Only the differences between the two segments are described in detail.

Dorsolongitudinal muscles:

dllach (B : 37), a thick muscle divided into two fasciculi a and b arising one above the other on the preseutum and both inserting on the postnotum. (B: 38), much thicker than IIdl2. The muscle arises on the anterior part of the scutum, lateral to dll and above the dorsoventral group. It inserts on the lateral tendon plate of the postnotum. Its extension therefore is not parallel to the dv- group as is the case in the mesothorax. (G :-; W : dlmz), a very thin flat muscle which extends between the anterior and the posterior ridge of the scutellum; it does not insert on the postnotum as is the case with the IIdl3 muscle. It also does not extend in a straight line, but lies directly under- neath and contiguous with the hypodermis following the vaulted chitin of the scutellum. On account of these differences its homology with the IId13 muscle appears to be doubtful.

Ventrolongitzidinal muscles: (B : 36a; W : vlml), a broad thick muscle which arises on the lateral tendon plate of the furca3 and inserts on the anterior edge of the fused sterna of the first two abdominal segments.

602 HANS NUESCH

v l g (B : -; W : -), a thick short muscle which extends between the postcoxal bridge and the lateral apodema of the first abdominal sternum.

Dorsoventral muscles: (B : XXXVI ; W : dvml) , undivided and thin in anterior-posterior direction. (B : 42; W: dvmz), thinner than dvl. (B : 46 ; W : dvma), corresponds to IIdv3 and is also divided into two fasciculi a t the dorsal origin. ( C : 43 ; W : dvm4), a thin muscle which arises in front of dvj, not, lateral t o it as in the mesothorax. (B : 43; W : dvm4), thinner than d\l4 and well separated from it.

Pleurodorsal niuscles : Is absent in the metathorax.

(B : 56 ; W : pm6), a large muscle corresponding to IIpds but with a somewhat different origin. Fasciculus a arises on the pleural wing process, fasciculus b on the episternun?, fasciculus c on the pleural ridge. The muscle inserts on the dorsal third axillary sclerite. (B : -; W : pm3), a thin muscle.

Pleuroventral muscles: (B : - ; W : -) , a thin muscle arising on the preepisternum and inserting on the anterior tendon membrane of the basalare. Therefore, i t corresponds only to the small anterior fasciculus of IIpv1. (E : XLVII ; W : pml) , a thick muscle corresponding to IIpvz but arising in part on the ventral end of the pleural ridge, not only on the basicosta. (B : -; W : pm,) , a very thin and long muscle. (B : XLIX; W : pm4) and pvi (B : XLIX; W : pmj), two thick muscles with exactly the same relationships as in the mesothorax. (E : 51 ; W : pm7) , a short flat muscle. (B : 65 ; W : -, but present in Papilio according to Maki), corresponds to IIpv7 except that the fibers arise on the furca3, and the long tendon inserts on the ventral end of the pleural ridge. Is absent in the metathorax. Pleural muscles: The pleural muscles I Ipl and IIp, have no homologues in the metathorax.

dvl

dvg dv3

dv4

dvj

pdl pd,,,,,,

pd3 pd4 and pdj Are absent in the metathorax.

pvl

pv2

pvs pv4

pva pv7

pv8


Sternopedul muscles: (W : bml), much thinner than the corresponding IIstl. (W : bm2), thick muscle. (W: bma), a flat muscle corresponding to IIsta, arising on the postcoxal bridge and inserting on the dorsocaudal edge of the meron. (W:-) is absent in the metathorax.

Coxal muscles:

to these in size.

Xpiracular muscles: Very thin dilator muscle extending between the posterior wall of the spiracle and the ventrolateral edge of the scutum. Thin short occlusor muscle arising without tendon on the furcaz and inserting on the ventral edge of the spiracle. The contraction brings a valve from the anterior side into the opening of the spiracle.

stl s t g st,3

st$

ex1, ex. and cx3 correspond to IIcxl, 11~x2 and 11~x3 and are similar

sd

so

Variation

Little variation was encountered in the musculature of different individuals. In most of the animals examined the muscles were precisely as described in the preceding pages. Only once was a muscle found to be completely absent, namely, the IIdI.. The skeletoii of this particular individual, especially the process on the laterophragma where this muscle ordinarily inserts, was normal. In one animal the IIIst, muscle was divided into two fasciculi with unaltered insertion, but with one fasciculus arising on the anterior part of the median ridge of the sternum the origin of the other part being normal. In another animal the IIIdv, muscle attached on the scutum lateral to dv3+* instead of between dv, and dv3. Other small variations are mentioned in the text (e.g., IIvll, IIpv,).

ACKNOWLEDGMENTS

The present study, and especially the experimental work referred to, was begun during a stay with Prof. C. M. Williams, Biological Laboratories, Harvard University, Cam- bridge, Mass. I wish to express my warm thanks to Professor

. 604 HANS N ~ ~ E S C H

Williams for valuable discussions, his aid and the material ; also to the Janggen-Pohn-Stiftung in St. Gall, Switzerland, which made this stay possible by a grant.

LITERATURE CITED

BERLESE, ANTONIO 1909 Gli insetti. Milano. MAKI, TAKADI 1938 Studies on the thoracic musculature of insects. Mem. Fac.

MALOUF, N. S. R. The role of inuscular contraction in the production of

NUESCE, H. Ueber den Einfluss der Nerven auf die Muskelentwicklung

SNODGRASS, R. E. 1935 Principles of insect morphology. McGraw-Hill Co.,

WEBER, H. 1928 Die Gliederung der Sternopleuralregion des Lepidopterenthorax

Sci. and Agric., Taihoku Imperial Univ., Formosa, $4: 1-343.

configurations in the insect skeleton. J. Morph., 58: 41-85.

bei Telea polyphemus (Lepid). Revue Suisse Zool., 59 : 294-301.

New York.

Zeitschr. wiss. Zool., 131: 181-254.

1935

1952

1933 Lehrbuch der Entomologie. Fischer, Jena. WILLIAMS, CARROLL M., AND HOWARD A. SCHNEIDEEMAN 1952 The necessity

of motor innervation for the development of insect muscles. Anat. Rec.. 123: 560

PLATES

PL

AT

E 1

EX

PL

AN

AT

ION

OF

FI

GU

RE

1 In

tern

al v

iew

of

the

righ

t ha

lf o

f th

e sk

elet

on o

f th

e he

ad a

nd t

he t

hora

x of

Te

lea

poly

phem

us.

x 11

.8.

at,

ante

rior

arm

of

the

tent

oriu

m

awp,

ant

erio

r no

tal

win

g pr

oces

s ax

, fi

rst

axil

lary

ba

, ba

sala

re

bat,

ten

don

cap

of

the

basa

lare

be

, ba

sico

sta

c, c

ervi

c.al

e ex

, co

xa

epm

, ep

iiiie

ron

eps,

epi

ster

num

ep

sf,

epis

tern

al f

issu

re

epsr

, ep

iste

rnal

rid

ge

f, f

urca

fr

, ri

dge

on t

he f

urca

ster

num

fs

t, f

urca

ster

num

ir

, in

ner

ridg

e on

the

scu

tum

la

, lat

eral

apo

dein

a of

the

fus

ed s

tern

a of

th

e tw

o fi

rst

abdo

min

al s

eg-

men

ts The

sub

scri

pts

1, 2

, 3,

I,

I1

abdo

min

al s

egm

ent,

res

pect

ivel

y.

m,

mer

on

sc,

scut

uin

inc,

mer

oeos

ta

scl,

scut

ellu

m

mw

p, m

edia

n no

tal

win

g pr

oces

s m

r, m

edia

n ri

dge

of t

he s

tern

um

pab,

pos

tala

r br

idge

ss

, sp

inas

tern

uin

pcxb

, po

stco

xal

brid

ge

st,

ster

num

ph

, ph

ragm

a st

cx,

ster

noco

xale

pl

r, p

leur

al r

idge

tb

, te

ntor

ial

brid

ge

plw

p, p

leu

~u

l win

g pr

oces

s tf

, te

rgal

fis

sure

pn

, po

stno

tum

tg

a, t

egul

ar a

rm

tr,

troc

hant

er

poc,

pos

tocc

iput

po

r, p

osto

ccip

ital

rid

ge

Vr,

V-s

hape

d ri

dge

pp,

prep

ectu

s pr

a, p

real

ar a

rm

psc,

pre

scut

uin

pscr

, pr

escu

tal

ridg

e pw

p, p

oste

rior

not

al w

ing

proc

ess

sa,

suba

lare

sa

t, t

endo

n ca

p of

the

sub

alar

e

sp,

spin

a sp

r, s

pira

cle

indi

cate

the

fir

st,

seco

nd,

thir

d th

orac

ic a

nd t

he f

irst

or

seco

nd

SK

EL

ET

ON

AN

D N

USC

LE

S O

F T

EL

EA

:>

PL

AT

E 1

PLATE 2

EXPLANATION O F FIGURES

2 to 5 Show the muscles in the right half of head, neck, and thorax of Telea polyphemus in 4 successive phases of dissection from the sagittal plane to the lateral wall. All other parts such as the nervous system and the tracheae have been omitted. X 8.5.

am, muscles moving the antenna cd, cervical dorsal pv, pleuroventral cv, eervical ventral ex, coxal so, spiracular oeclusor d, dorsal st, sternopedal dl, dorsolongitudinal t, tentorial dv, dorsoventral v, ventral p, pleural vl, ventrolongitudinal

I, 11, I11 indicate the first, second, and third thoracic segment, respectively.

pd, pleurodorsal

sd, spiracular dilator

608

SKELETON A N D MVSCLES O F TELEA IL4NS NUESCII

PLATE 2

609

the morphology of the thorax of telea polyphemus (lepidoptera). i. skeleton and muscles

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