The pleuron in most insects bears three inwardly directed processes for the attachment of muscles. These usually comprise a dorsal pleural wing process for articulation of the wing; a lower lateral pleural coxal process (Pcp) with which the coxa articulates; the pleural suture and pleural ridge (entopleuron) (Er) extending through it; and the pleural arm (Pa) which is situated a short distance above the coxal process, projecting inward and downward from the entopleuron to rest against the furca and thus form an internal connection between the pleuron and sternum.

Macropathus filifer being apterous lacks the pleural wing process, and in the propleura the pleural arm is missing from the entopleuron. In the three segments the epimeron is considerably reduced, while the episternum is large. The episternum is subdivided longitudinally and has a thickened ventral margin. In the prothorax only it is fused with the precoxale which passes ventrally to unite, but not fuse, with the sternum and thus form a bridge connecting the episternum to the sternum. The precoxale is absent from the mesothorax and metathorax.

Articulating with both the antero-mesal margin of the coxa and the anterior end of the thickened ventral margin of the episternum is a small, transversely placed, triangular-shaped sclerite, the trochantin (T).

Between the thoracic segments, situated within the intersegmental membrane, are the intersegmentalia, the sclerites which surround the spiracle. The third thoracic spiracle belongs to the first abdominal segment. Snodgrass (1935a) says that the first and second spiracles belong to the mesothorax and metathorax respectively, although they often “migrate forward during development and come thus to have a definitive position in the secondary intersegmental membranes or in the posterior parts of the segments preceding them. The meso-thoracic spiracles particularly are subject to this anterior migration and hence often occur in larval or adult insects on the sides of the prothorax, for which reason they are frequently called the ‘pro-thoracic’ spiracles. “In Macropathus filifer the spiracles have moved forward into the posterior part of the pro-thoracic and mesothoracic intersegmental membranes and the mesothoracic spiracle is much larger than the metathoracic one.

Sternum. Figs. 17, 18. The prosternum of Macropathus filifer is divided into four parts—prosternite (Pt), verasternite (V), fureasternite (F) and spinasternite (St). The prosternite is absent in the mesosternum and metasternum but the other three sclerites are present. Martin (1916) says the sternum of insects is “composed of five subdivisions,” but the fourth division, the post-furcasternite, is not present in M. fiilifer.

Prosternum. Anteriorly this consists of a poorly chitinized area formed from a membrane with rings of chitin embedded in it (Pt), which extends into the cervicum. Situated immediately posterior to this is the verasternite (V), which is produced at each anterior corner into a long arm directed antero-laterally. The verasternite is connected by a narrow membrane with the precoxale (Pc), which is fused to the episternum (E) forming the precoxal bridge. There is no postcoxale. The furcasternite is situated directly behind the verasternite, from which it is separated by a membrane. Anteriorly it is divided into two short processes and internally it bears the furca (Af) which consist of two long, slender, anteriorly directed arms, each terminating in a thin plate. The spina-

sternite is very small and oval and bears the single, median, star-shaped spine (Ms), consisting of five approximately equal arms.

Mesosternum. The verasternite, furcasternite and spinasternite are all fused together forming one large plate. The posterior margin bears the medifurca (Mf) and the median spina. There is no precoxale. The medifurca consists of a stalk attached to the furcasternite and bearing two laterally diverging arms, each one of which bears three processes directed anteriorly, antero-laterally and posteriorly respectively. The antero-lateral of these processes is the largest, and it articulates with the pleural arm (Pa) of the entopleuron on its side. The spina is attached by a stalk to the spinasternite and bears five arms—two large ones antero-laterally, two small ones anteriorly, and one large one posteriorly.

Metasternum. The small oval verasternite lies partly in a median depression of the furcasternite from which it is separated by a membrane. The furcasternite is large and bears two anteriorly directed arms. The spinasternite is reduced to two very small sclerites at the base of the furcasternite. The metafurca (Mtf) which is attached to the furcasternite consists of a stalk bearing two laterally diverging arms. Each arm bears three processes directed anteriorly, postero-laterally and posteriorly respectively. The postero-lateral process is the longest, and it articulates with the pleural arm of the entopleuron. Attached to the spinasternite is the median spina consisting of five arms—two long ones directed antero-laterally, two shorter ones postero-laterally, and a much shorter one posteriorly. Of the spinasternite Martin (1916) says, “It is so variable in position that it is very hard to tell to which segment the spinasternite belongs, but it probably belongs to the segment in front of it, as no spinasternite has ever been described as occurring in front of the prothoracic verasternite.” In M. filifer this is true, for the spinasternite is definitely the last sclerite of each segment. In contradiction to Snodgrass (1935a). who states: “It should be observed that the metasternum never has a spinasternite, because the third intersternite either is suppressed or becomes the acrosternite of the first abdominal sternum”, M. filifer has a small spinasternite to which is attached a well developed spina.

Cervical Sclerites. Fig. 17. There are three pairs of lateral cervical sclerites (Lc). The anterior one is oblong and in front articulates with the margin of the occipital foramen to which its anterior end is connected by a membrane. Posteriorly it articulates with the forward edge of the triangular-shaped second sclerite, and this in turn articulates with the third sclerite which is the largest of the three. This third sclerite bears a large postero-lateral arm and articulates behind with the precoxal bridge.

There are two pairs of oval shaped ventral sclerites (Vc) embedded in the membrane of the neck, the posterior pair being more strongly chitinized than the anterior pair.

Legs. Figs. 21-23. The legs are long and slender The fore and middle limbs are about the same length, but the hind limb is much longer and more powerfully constructed for jumping. Each leg consists of six articulating segments—coxa (C), trochanter (Tr), femur (F), tibia (T), tarsus (Ta) and pretarsus (Pta). Crampton (1923) states, “The trochanter articulates with the coxa but does not articulate with the femur in any insect I have examined, and it is quite possible that the trochanter may be a constricted off portion of the femur.” Maskell (1927) says, “In the metathoracic legs of Hemideina the

trochanter is firmly attached to the femur, there being no articulation between them. But in the prothoracic and mesothoracic legs there is a small but distinct articulation between trochanter and femur”. In Macropathus filifer there is a definite articulation between the trochanter and femur in all three pairs of legs. It is especially noticeable in the metathoracic legs where the articulation is easily broken and the legs lost, while the coxa and trochanter remain attached to the thorax. Auditory organs are lacking on the prothoracic tibia, and because of this there is no area of small spines on the femur of the hind leg, nor a file

Text-fig. 4. Thoracic Appendages.—Fig. 21—Left hind leg. Fig. 22—Left middle leg. Fig. 23—Left fore leg.
A, apical spine; Asp, apical spur; C, coxa; F, femur; Pl, pseudopad, but euplantula lacking; Pta, pretarsus; Sa, subapical spine; T, tibia; Ta, tarsus; Tr, trochanter; U, unguis