G. C. Crampton.
The Thoracic Sclerites and Wing Bases of the Roach Periplaneta americana and the Basal Structures of the Wings of Insects.
Psyche 34:59-72, 1927.

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PSYCHE
VOL. XXXIV. APRIL 1927 No. 2
THE THORACIC SCLERITES AND WING BASES OF THE ROACH PERIPLANETA AMERICANA AND
THE BASAL STRUCTURES OF THE
WINGS OF INSECTS
Massachusetts Agricultural College, Amherst, Mass. The head and abdominal structures of the American roach have been described in Vol. 32, p. 195 of Psyche for 1925. In
the present paper the thoracic sclerites and wing bases of the roach are discussed, and certain previously overlooked struc- tures in the basal region of the wings of insects in general are described, since they appear to be of considerable interest from the standpoint of phylogeny and the interpretation of the wing veins
In examining the thoracic sclerites, it is preferable to study them in relation to the internal structures for muscle attach- ment, etc., and with this purpose in view, the dorsal (or the ventral) region of the thorax should be cut away, and the parts should be boiled in 10% caustic potash to remove the muscles and other soft parts, which may be washed away with a pipette. The parts should be studied immersed under water or alcohol, and the field of the binocular should be illuminated by a brilliant light provided with a bulls-eye condenser. The neck ("cervicum" or eucervix) is a demarked anterior portion of the prothorax, whose membranous walls permit greater freedom of movement for the head. Its sclerites, called the cervical sclerites (cervicalia) are homologous with the in- tersegmental plates (intersegmentalia) occurring between the thoracic segments in certain Apterygota, and, according to their position, they are called the dorsal, lateral and ventral cervicals. Ps\che 3459.75 (1927). hup //psyche rinclub org/14/14-059 html



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60 Psyche [April
The ventral cervicals pgu and is of Figs. 1 and 5 are narrow, transverse sclerites, homologous with the sclerites called the postgulare and intersternite by Crampton, 1926. The lateral cervicals 1c of Figs. 1 and 5, are the largest neck plates, and each is made up of three parts, or subdivisions. The anterior sub- division ec bears a cephaliger cq or process which articulates with the occipital condyles occ of the head. The median lateral cervical ic touches its fellow of the opposite side in the median ventral line of the body, in the fashion characteristic of most roaches, mantids and termites. The posterior lateral cervical area poc is inflexed and bears a small internal protuberance at the point f of Fig. 5. The small sclerite t of Figs. 1 and 5 may be included with the lateral. or with the dorsal, cervicals. The dorsal cervicals pr (Fig. 15) are small and unimportant, but the dorsal cervicals it are quite large and unite posteriorly to form a horse-shoe-shaped area bearing a pair of internal protuberances. The posterior dorsal cervicals (or postintertergites) bear the internal tendons et (Fig. 15) for muscle attachment. The sternal region of each thoracic segment (excepting the metathorax) contains three typical sternites or sternal sclerites as follows. The basisternite bsl, bs2, and bs3, of Fig. 1, is the principal sternite and is usually connected with the episternal region es by a precoxal bridge pc. In the mesothorax and meta- thorax, the basisternurn bs2, and bs3, of Fig. 1 is composed of an unpaired median portion and two lateral halves. The furcasternite (or furca-bearing sternite) fs 1, is subtra- pezoidal in the prothorax, but it is shaped like an inverted "Y" in the nieso- and metathorax. The furcasternite fs (Fig. 1) bears the furcal pits, or furcacavse fp, which are the external manifestations of the invaginations forming the internal diapo- physes, or f'urca fu, of Fig. 5. These paired apophyses, or diapo- physes (furca), serve to hold the nerve chain in place, and they furnish attachment for muscles etc. Miall and Denny in their book on the cockroach failed to find the prothoracic furca fu of Fig. 5, but these structures are quite well developed in the pro- thorax, and are composed of a delicate shaft, or basifurca, and a broad distal portion, or distifurca, which extends to the apodeme ap of the pleural region.




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. 19271 Thoracic Sclerites and Wing Bases of the Roach 61 The spinasternite ss of Figs. 1 and 5 is not very greatly elongated in the prothoracic region, but in the 'mesothorax it is long and slender. The spinasternite of the metathorax is atro- phied, or it is indistinguishably united with the furcasternite fs, in this region. The spinasternite ss of Fig. 1, bears the spinal pit, or spinacava sp, which is the external manifestation of the invagination forming the internal, median, unpaired apophysis called the monapophysis, or spina spi, of Fig. 5, which serves for muscle attachment etc.
The internal sternal processes, such as the furca fu and spina spi, may be called the endosterna, and as was mentioned above, these endosterna serve tor the attachment of muscles etc. As was suggested by Crampton, 1918, instead of designat- ing muscles by their function etc., it is preferable to designate them by their points of origin and insertion; and if this method be followed, we may speak of the furco-apophysal muscles, the furco-coxal muscles, furco-trochanteral muscles, etc., or the profurco-mesofurcal muscles, prospino-mesospinal muscles, etc., and the terms are self-explanatory.
In the three thoracic segments (Fig. 1) a pre-coxal bridge composed of the sclerites pc and ac connects the basisternite 6s with the episternum es. The sclerite pc is very loosely connected with the pleural region in the meso- and metathorax, and may possibly represent the sclerite called the lateropleurite, while the sclerite ac which is well developed and is connected with the sternal region in the mseo- and metathorax, may represent the laterosternite; but provisionally, at least, I have followed- the interpretations indicated by the labelling, (see list of abbre viations) until the matter can be definitely determined. In the meso- and metathorax, a ventral prolongation of of the suture s (Fig. 1) demarks the preepisternum pes or an- terior marginal sclerite, which bears an internal protuberance for muscle attachment. In front of this region is a "dimple- like" impress, or depression labelled i in Fig. 1, which marks the location of an internal tumulus, or protuberance labelled en in Fig. 5, to which certain muscles are attached .An infolding (or "inpocketing") of the integument of the pleural region forms an internal ridge, or endopleuron ep of Fig.



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62 Psyche [April
5, while the external lips of the fold meet to form the pleural suture ps of Fig. 1, which demarks the epimeron em from the episternum es. At the ventral end of the pleural suture ps of Fig. 1, is the coxifer cf, or coxa-bearing process, while at the dorsal end of the pleural suture ps is the alifer o, or pleural ful- crum of the wing. Internal processes of the coxifer labelled ecf 3 in Fig. 5, and internal processes of the alifer, labelled ea 2 in Fig. 5, are fairly well developed in the roach; and the endo- pleuron ep of Fig. 5 gives off an apodeme, or process up, rather closely associated with the furca fu.
In the meso- and metathorax, there occurs in front of the pleural suture ps of Fig. 1, a suture r, which divides the epis- ternal region es into an upper region aes, or anepisternite, and a lower region, or katepisternite (bearing the label es in Fig. 1). An anepisternal incision aei divides the anepisternite into an anterior and posterior region. The basalar sclerites x and u, situated dorso-caudad of the anepisternal incision aei (Fig. I), are portions of the pleural region. The anterior basalare u of Fig. 1 is demarked by the suture s, and it bears an internal process eb of Fig. 5. The posterior basalare x of Fig. 1 is a de- tached portion of the pleural region in front of the alifer o, and both of the basalar sclerites are associated with the movements of the wing in flight.
Above the alifer o of Fig. 1 is the intraalare ia (See also Figs. 13 and 14), which is an alar ossicle connected with the dorsal alar ossicle a of Fig. 16 (Compare also Figs. 13 and 14). The sclerite ia may be a detached portion of the wing structures, but it is hardly a detached portion of the pleural region. The subalare sa of Fig. 1, however, may have been formed by the deposition of chitin in the membrane below the wing, for the attachment of the mero-subalar muscles extending between the meral region of the coxa and the subalar plate in question. The trochantin, bearing the labels atn and ptn in Fig. 1, is a triangular plate in front of the coxa, and the trochantin bears at its tip an internal trochantinal tendon ttn of Fig. 5, for muscle attachment. A trochantinal suture, with its corresponding in- ternal ridge or endotrochantin etn of Fig. 5, divides the trochantin of the meso- and metathorax into an anterior region atn and a



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19271 Thoracic Sclerites and Wing Bases of the Roach 63 posterior region ptn (Fig. 1)) while a transverse "break," or cleft, divides the prothoracic trochantin into a basal region bin and a distal region, dtn, as is also the case in other roaches, mantids and termites, etc. In such cases, the small distal region dtn is usually interpreted as the entire prothoracic trochantin, al- through the basal portion btn also belongs to the prothoracic trochantin. The trochantin of all segments is closely associated with the pleural region (from which it is separated by the pleuro- ttochantinal suture p of Figs. 1 and 5) and it may be a detached portion of the pleural plate. On the other hand, it is maintained by several investigators that the troch,antin (or even portions of the pleural plate itself) is a detached basal region of the leg, to which the term subcoxa is sometimes applied. Between the trochantin and the coxa is a small sclerite pac called the, paracoxale, which bears an internal paracoxal tendon pat (Fig. 5) for muscle attachment. . The sclerite pac is either a detached portion of the marginal region of the coxa, or it was formed in the membrane between the trochantin and coxa, to bear the internal tendon pat for muscle attachment. Behind the
coxa is an internal tendon pt (Fig. 5) called the postcoxal tendon, to which are attached , certain muscles. A faint "impressy)
marks its location externally.
In the prothorax, a marginal region, the basicoxale be of Fig. 1, is demarked in the basal region of the coxa. Its anterior region cm has been termed the coximarginale, and its posterior region me is homologous with the meron me of the other legs. An internal ridge, or endocoxa, demarks the region be internally, and serves for the attachment of muscles, as described by Dr. R. E. Snodgrass. In the meso- and metathorax, the meral region me2 and me3 is much more extensive than in the prothorax (i. e. me of Fig. I), and a meral ridge, or endomeron mr of Fig. 5, serves to demark the meral region internally-andit also serves as a ridge for muscle attachment. The parts of the leg of a roach, together with their tendons, method of articulation, etc., have been described in a paper by Crampton, 1923 (Can. Ent. LV, p. 126), and need not be further discussed here, since the appendages of the thorax will be described more fully in a paper dealing with the legs and wings of the roach.



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64 Psyche [April
The spiracle st between the pro- and mesothorax (Figs. 1 and 5) is mesothoracic in origin, and should therefore be spoken of as the meso-thoracic spiracle, despite the fact that it is very closely associated with the prothoracic region. The second spiracle is metathoracic, and the third one is the first abdominal spiracle. The mesothoracic spiracle is usually located in the membranous region continuous with that containing the spina- sternite ss (Figs. l and 5)) particularly in larval forms, and this may indicate that the supposed prothoracic spinasternite is mesothoracic rather than prothoracic. In any case, this sternite may be referred to as the spinasternite, although if it belongs to the mesothorax (as its association with the spiracle in other insects seems to indicate) the term poststernellum, applied to it by some investigators, is hardly applicable, since it would then be the anteriormost mesothoracic sternite, instead of the post- eriormost prothoracic sternite (as the name "poststernellum" would indicate). The relation of the spiracles to the thoracic sclerites, the mechanism of the thoracic spiracles, and similar topics will be discussed in a paper dealing with the respiratory system of the roach, and nfeed not be further discussed here. As is shown in Fig. 12, the pronotal plate or "pronotum" is divided into a disk or central portion labelled disc and a mar- ginal region or limb labelled limb, whose lateral areas are called paranoia. The ventral inflexed margins of the pronotum are closely applied to the dorsal surface of the pronotum (above) and the edges of these margins apparently exert a tension, re- sulting in the formation of faint lines such as those indicated by the dotted lines bordering the disk of the pronotum shown in Fig. 12. In the discal region, labelled disc, are several muscle- scars, or myocicatrices, etc., which need not be further discussed at this time, since they 'will be described in a paper dealing with the muscular system of the roach. The pronotal plate probably corresponds to the eunotum (or wing bearing plate) of the other thoracic segments, in which a prescutum, scutum and scutellum are secondarily demarked in the eunotum of the meso- and rnetathorax, but these areas are not demarked in the pronoturn. The poorly chithized and pigmented area labelled psi1 in Fig. 16, probably represents the postscutellum of the other thoracic



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19271 Thoracic Sclerites and Wing Bases of the Roach 65 segments (in which the postscutellum is formed behind the eunotum or wing-bearing plate). The small anterior margin of the mesonotum bearing the label pm in Fig. 16 may be considered as a posterior portion of the prothorax, since, as Dr. Snodgrass points out, the phragmas represent the lines of demarcation be- tween the segments dorsally, and the area pm of the mesonotum (Fig. 16) lies in front of the phragmas (or internal structures for muscle attachment, whose location is indicated by the pits ppt of Fig. 16) and should therefore be reckoned to the prothoracic region, although it is borne on the anterior margin of the meso- notum.
In the meso- and metanotal region, the wing bearing plate, or eunotum, is divided into the following regions. The anterior- most sclerite, or pretergite,prt of Fig. 16, is an ill-defined region bearing the phragmal pitts ppt which mark the location of the internal ridges or phragmas ph of Fig. 13, for example, and these phragmas or phragmal ridges delimit the segments dorsally, so that the anterior marginal region pm of the pretergite being anterior to the phragmas, belongs to the segment in front, as was mentioned above. In the mesonotum of the roach (Fig. 16) the prealar sclerite pro becomes detached from the lateral region of the pretergite prt, while in the mesonotum of the mantid shown in Fig. 6, the region pra forms an incomplete prealar bridge, which is well developed in such insects as the Plecoptera, etc. In the metanotum of the roach (Fig. 16) the prealar sclerite pra does not become detached (as it does in the mesonotum) but it bears a pit like that labelled pp in the prealar sclerite pra of the mesonotum. The anterior margins of the sclerites prt and pra apparently become involved in the formation of the postscu- tellum of the segment in front, when the postscutellum is en- larged throutgh fwther chithization and pigmentation of the "intersegment al" membrane to form the large postscutellar plate of other insects
The faintly demarked median region labelled psc in the mesonotum of the roach (Fig. 16) corresponds to the prescutum of the mantid shown in Fig. 6, and represents the second im- portant area demarked in the eunotum (or wing-bearing plate). The regions labelled pn2 and pn3 in the meso- and metanotum



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66 Psyche [April
of the roach (Fig. 16) are probably secondarily-formed areas demarked by a rather faint suture pns, with its corresponding internal ridge epn2 of Fig. 13. These structures are extremely faint in the metanotum (Fig. 16).
The scutellum of the mesothorax sl2 is greatly elongated and extends to the prescutal area psc of Fig. 16. In the meta- thorax, however, the scutellum sl3 is shorter and a suture-like structure mds of Fig. 16 connects it with the prescutal region. The scutellum sl2 (Fig. 16) is a demarked area of the eunotum . bounded laterally by the scutellar sutures sls with their corres- ponding intern1 ridges etc., labelled es12 in Fig. 13 Behind the scutellum sl2 (Fig. 16) is the posttergite pot, which is formed by a posterior fold, or reduplication, of the wing-bearing plate, or eunotum. Behind this are the post- scutellar plates psi (Fig. 16)) which encroach upon the mem- branous region, in other insects, and finally incorporate the marginal region pm, in front of the phragmal pits ppt, to form the large postscutellum of higher insects, in which the post- scutellum may appear to bear the phragma. The postscutellum of the roach is but feebly developed and is represented by the small plates bearing the label psi in Fig. 16. These plates are formed behind the wing-bearing plate, or eunotum, whose post. erior margin is continuous with the posterior margin of the wing. In the eunotum, or wing-bearing plate, the scutum sc (Fig. 16) is very large and it occupies the greater part of the eunotum. It bears an anterior wing process, or suralare sur (which may be a lateral portion of the region prt in some insects), and a posterior wing process, or adanale ad (Figs. 16, 6 and 10)) in front of which is an important incision ni, serving to divide the scutum into an anterior region and a posterior region, the latter being practically equivalent to the region called the parascutellurn in other insects. The incomplete sutures extending mesad from the incision ni in Fig. 16, correspond in a general way to the transscutal sutures, dividing the scutum into an anterior and posterior region in certain insects.
A tegular incision ti of Fig. 6, usually separates the prealar sclerite pro, from the suralar sclerite sur, and the tegula tg is located at the mouth of the incision in most insects (Figs. 6, 10,



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19271 Thoracic Sclerites and Wing Bases of the Roach 67 13, 16, etc.). The tegula tg (Figs. 6 and 16) is probably formed by the deposition of chitin and pigment in the membrane near the tegular incision ti, but the parategula, or basicostale ptq2 (Figs. 6 and 16)) is probably a detached basal portion of the costal region (or vein) of the wing.
Behind the suralar sclerite sur of Figs. 6, 10, 16 etc., is the suralar incision si and the alar ossicle labelled n in these figures, which is called the notale, or notopterale, is located in the neighborhood of the incision si. The alar ossicle n appears to be a detached portion of the notum. It is prolonged anteriorly into a neck-like, slender portion, whose "head" abuts against the end of the sclerite scc. The sclerite scc is a demarked "head" of the subcostal vein, and is the dorsal portion of the subcostale d (Figs. 1, 13, etc.) located on the under surface of the wing. The medialia, or median ossicles a, b and c of Figs. 6, 10, 16 etc., intervene between the ossicle n, and the base of the wing- veins radius and media. The proximal mediale a, is separated from the ossicle n by the cleft run of Fig. 16, and ossicle a sends down a ventral prolongation ia of Fig. 14, to form the ossicles labelled ia in Fig. 1, which are located just above the alifer o (the wing-bearing process of the pleuron). The incision in of Figs. 6 and 16 separates the ossicle a'from ?ssicle 6, which is usually, closely associated with the ossicle ba of Figs. 6, 10 and 16. The suture (or cleft) im of Figs. 6, 10 and 16, separates the intermediate median ossicle b from the distal median ossicle c. Ossicle c, in turn, is separated from the head of the vein labelled mca, by the suture labelled rns in Figs. 16, 6 and 10. The basanal ossicle ba of Figs. 16, 6, 10 etc., usually ar- ticulates with the posterior notal wing process, or adanale ad, at one end, while at the other end, it is associated with the ossicle a, and is usually united more or less closely with ossicle b (see also Fig. 14). The anale, or anal ossicle an of Figs. 6, 10 and 16, intervenes between ossicle ba and the base of the anal region in the fore wing of the roach, mantid and termite here figured. Faint traces of a postbasanal ossicle may be seen behind the ossicle labelled ba, in the metanotum of the roach shown in Fig. 16.
In the fore wing of the roach shown in Fig. 16, the mantid



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68 Psyche [Aprf I
shown in Fig. 8, and the termite shown in Fig. 10, the anal, or claval, area aa of the tegmen (fore wing) is connected with the notum by a region called the alula, or jugalula ja which may be involved in the formation of the jugum etc., of higher insects. An axillary ridge, or a crack-like rima po (Figs. 6 to lo), sep- arates this region from the anal or claval region aa (Figs. 6, 7, 8, 9, 10, 16 etc. and the veins which are located behind this line of demarcation (i .e. such as those labelled ax in Figs. 8, 9, etc.) should be referred to as the axillaries or axillary veins. The
faintly chitinized and pigmented areas labelled ju in Figs. 6, 10 and 16, are formed in the basal region of the alula; and the sclerite behind the metathoracic ossicle ba of Fig. 16, may be associated with these areas of the fore wings. The sclerite pju of the hind wing of the roach (Fig. 16), however, seems to be formed behind the area containing the region ju in the fore wing (Fig, 16), and is connected with a different portion of the notum by a narrow neck as is shown in Fig. 16. The relation of these parts to the calipteres of Diptera, etc., will be discussed in another paper.
In studying the fore wing of the roach I noticed a basal, ridge-like fold bp and a deep "marsupium" or basal sinus bsi (best seen after boiling the parts in caustic potash to spread them apart more readily), such as that shown in the tegmen (modified fore wing) figured in Fig. 16 These structions are very prominent, but have been apparently overlooked before, although they occur in a great many of the insects descended from the ancestral types included in the common Protorthop teron-Protoblattid stem-e. g. in such insects as those shown in Figs. -11, 16, 7, 8, 9, and 10. I do not find this basal fold and sinus in such insects as the ephemerids and Odonata which cannot lay their wings back along the top of the abdomen in repose, while the descendants of the groups which can do this (see division of insects into two groups on this basis in Vol. 16 p. 33 of the Journal of Ent. and Zoology for 1924, or papers in the Transactions of the Amer. Ent. Society,,LII, 1926,p. 239) show distinct traces of the fold and sinus (as I have also pointed out in the Bull. Brooklyn Ent. Soc., 1927, XXII, p. 1) so that the presence of these structures is of considerable importance



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19271 Thoracic Sclerites and Wing Bases of the Roach 69 from the standpoint of phylogeny, and these structures likewise serve as landmarks in determining the location of certain veins, ,
areas etc., of the wing. The basal fold bp and pocket-like sinus bsi are very prominent in the fore wings of roaches, termites, the Hemiptera with coriaceous fore wings, etc., and it is very probable that these structures were developed in order to fa- cilitate the folding back of the fore wings, when these are laid along the top of the abdomen in repose (see Bull. Brooklyn Ent. Soc., 1927). I shall again refer to these structures in a paper dealing with the basal region of the wings of insects in general, so that it is not necessary to discuss the matter further at this time. As was mentioned above, a postanal, or postclaval ridge (or in some cases a rima, or crack-like line) labelled po in Figs. 6, 7, 8, 9, 10 and 16, demarks the axillary, or alular region, from the anal, or clayal region of the fore wings. A preanal, or preclaval rima cl demarks the anal area of the wing from the median region of the wing, and the rima cl may be regarded as a "rima dividens" paralleling the "vena dividens" described by Comstock and others, in this region of the wing. A median rirna, in front of the rima labelled cl in Figs. 10 and 16, demarks the median area of the wing from the radial area, in some insects, and a costal area ca of Fig. 16, is frequently demarked by the subcostal vein Sc in roaches, termites etc.
On the under side of the fore wing of the roach, as shown '
in Fig. 2, there is an important ventral ridge, the subcostal crista or plica scr, extending along the subcostal vein, and the condition exhibited in this region of the fore wing of the roach is of considerable interest from the standpoint of phylogeny, since the tegmen (fore wing) of the roach offers a very suitable startingpoint for tracing the modifications in this area of the elytra of beetles and the fore wings of other insects descended from roach-like forebears in the common Protorthopteran-Pro- toblattid stem.
When the fore wing of the roach is laid back in repose, it assumes the position shown in Fig. 2; and a protuberance m of the epimeron em 2 fits into a cavity in which the sclerite d at the base of the subcostal vein (or subcostal ridge scr) is located. The subcostal ridge scr lies above, and mesa1 to, the projecting