NO. 6 



INSECT ABDOMEN — SNODGRASS 



69 



mous by a suppression of the endopodite (B, Endpd), or by its con- 

 version into a genital process. In such cases the functional or loco- 

 niotory shaft of the appendage is the exopodite {Expd) . A crustacean 

 limb of this type of structure furnishes an analogy with the abdominal 

 limbs of Thysanura on the assumption that the stylus of the latter 

 (fig, 31 A, Sty) is the exopodite, and that the endopodite has been 

 entirely suppressed, or preserved only in the gonapophyses of the 

 genital appendages (B, Gon). 



End Cxpd(LB) 



ripd 



Fig. 28. — Ahdominal appendages of Crustacea. 



A, Apus longicandata, appendage from posterior part of body, left, anterior 

 surface. B, Anaspidcs iasmaniac, third abdominal appendage of left side, anterior 

 surface. C, Spirontocaris grocnlandicns, abdominal appendage of left side, 

 anterior view. 



Bud, basendite ; Bspd, basipodite ; Cxpd, coxopodite, or limb basis ; Endpd, 

 endopodite; Expd, exopodite; LB, limb basis, or coxopodite; Prtpd, protopodite 

 (united basis and basipodite) ; Tlpd, telopodite. 



The genital claspers of the higher insects, which are clearly homo- 

 logues of the abdominal styli of the Thysanura, may thus be 

 likened either to the gonopods of the Chilopoda (fig. 27 C, G/j), if we 

 assume that they are the main shafts of the telopodites, or to the ab- 

 dominal appendages of such crustaceans as Anaspides (fig. 28 B), 

 if we assume that they are exites of the appendages. As will later be 

 shown, however, it is difficult to obtain positive evidence as to the 

 nature of the insect abdominal styli ; whether they are likened to the 

 main shaft of the telopodite or to an exopodite branch depends largely 

 on the student's bias toward a myriapodan or a crustacean ancestry 

 for the insects. 



