NO. 6 INSECT ABDOMEN — SNODGRASS II5 



the Orthoptera they are undoubtedly outgrowths of the parts of the 

 definitive sterna derived from the bases of these appendages. 



Verhoeff (1903), retaining his former views on the homologies 

 between the abdominal and thoracic appendages, but going more into 

 detail, proposed, on theoretical grounds, that the stylus-bearing plates 

 of the insect abdomen represent the coxae, which in the abdomen 

 he distinguished as " coxites," or in the genital segments as " gono- 

 coxites." According to Verhoefif's theory, the telopodites are lost 

 from all the abdominal appendages except those of the eighth and 

 ninth segments, where they become the gonapophyses ; the styli are 

 secondary lateral outgrowths of the coxae, equivalent to the coxal 

 spurs of the thoracic legs of MacJiilis; and the eversible vesicles are 

 median coxal structures comparable with the coxal glands of Dip- 

 lopoda. 



Borner, though at first taking Heymons' view of the nature of the 

 gonapophyses, later (1904) agrees with Verhoefif that the genital 

 processes represent the telopodites of the abdominal appendages, pre- 

 served only on the gonopods. Regarding the supporting plates, how- 

 ever, Borner differs from Verhoeff in that he identifies them as 

 " basipodites," meaning by this term that each plate is the equivalent 

 of the coxa and subcoxa of a thoracic leg. (The same idea concerning 

 the nature of the basal plates is followed in the present paper, but 

 Borner's term " basipodite " is replaced with " limb basis " to avoid 

 confusion with the more usual application of the other word to the 

 first trochanter.) 



Silvestri (1903, 1905) regards the basal segment of an arthropod 

 limb as being in all cases a subcoxa (including the so-called coxop- 

 odite of Crustacea), and he would divide the appendage into a basis 

 (subcoxa) and a telopodite at the subcoxo-coxal joint. Applying this 

 interpretation of the basal structure of the limb to the abdominal 

 appendages of insects, Silvestri (1905) identifies the stylus-bearing 

 plates of the Thysanura with the subcoxae. The styli he regards as 

 the rudiments of the telopodites, with their bases representing the 

 coxae. Silvestri, therefore, admits no homology between the abdominal 

 styli and those of the thorax in Machilis; the leg styli he claims are 

 secondary outgrowths of the coxal integument. Verhoeff (1903) had 

 figured a coxal muscle attached to the leg stylus of Machilis, but 

 this supposed muscle Silvestri shows does not exist — an observation 

 in accord with statements by earlier as well as by subsequent writers, 

 and one easily verified. 



The most interesting feature in Silvestri's interpretation of the 

 morphology of the abdominal limbs is his proposal that the genital 

 8 



