NO. I 



INSECT THORAX — SNODGRASS 



95 



There is such uniformity of structure in the articulation between 

 the usual first and second segments of the leg that this joint may be 

 taken as invariably separating the coxa and the first trochanter. There 

 is no apparent reason for doubting that the second and third segments 

 of the chilopod leg (fig. 42 B) correspond with the basipodite and 

 ischiopodite of the crustacean leg (A). The first of these segments 

 lacks muscles in the Chilopoda, btit this is explained by Verhoeff 

 (1903a) as a device for allowing the leg to be broken off without 

 injury to the animal, the natural break taking place at the base of 

 the segment in the Pleurostigma and at the distal end in the Noto- 

 stigma. In insects there is reason for Ijelieving, as already shown 

 (page 78), that the basipodite and ischiopodite, or first and second 



~Tb+Tar 



Fig. 43. — Segmentation and nnisculature of legs of coleopteran larvae. (Figures 

 from Jeanne!, 1925, but differently interpreted, and re-lettered.) 



A, leg of larva of Trcchus, with usual six segments; B, leg of larva of 

 Bathisciins, with five segments. Cx, coxa; Dae, dactylopodite ; F, femur; S, 

 levator of tibia, T, depressor of tibia ; Tar, tarsus ; Tb, tibia ; Tb -\- Tar, tibio- 

 tarsus ; U , levator of tarsus ; V , depressor of tarsus ; A', X, branches of depressor 

 of dactylopodite ; x, tendon of A', inserted on base of dactylopodite. 



trochanter, have tmited to form the usual single trochanter (fig. 

 42 C). The presence of a reductor femoris muscle in the trochanter 

 identifies the trochantero-femoral joint with that between ischiopodite 

 and meropodite in Crustacea and Chilopoda (A, B). 



The principal bend, or " knee," in the telopodite of the arthropod 

 leg is regarded by Borner as being in all cases the joint between 

 meropodite and carpopodite. Jeannel (1925) takes exception to this 

 view, since he believes that in insects the tibia and the tarsus are 

 subdivisions of the propodite, and that the carpopodite has been lost 

 from the leg of all insects, except in those coleopteran larv.ne of the 

 Adephaga group that have six segments in the leg (fig. 43 A). In 

 other larvae, he claims, the six segments result from a division of 

 the propodite into tibia and tarsus. Jeannel would find a remnant of 

 the carpopodite in the small sclerite of the ventral membrane of the 



