NO. 6 INSECT ABDOMEN — SNODGRASS 83 



region of the body segment, instead of in the bases of the appendages, 

 as in the Thysanura (fig. 32 B, rvs). On the other hand, as we shall 

 presently see, the gill tubercles of the Corydalus larvae are almost 

 identical in structure with the abdominal feet of lepidopterous larvae. 



The appendages of the last abdominal segment in the larva of 

 Cliaidiodes and Corydalus are remarkable structures in that they com- 

 bine the characters of the preceding appendages of Corydalus with the 

 features of an abdominal leg of a caterpillar. Each of these termmal 

 appendages (figs. 35 D, Pp, 36 B, E) consists of a large, hollow, 

 somewhat cylindrical lobe of the body wall. The basal part of the 

 organ (fig. 36 B, E, LB) bears laterally a tapering process (Sty) 

 similar to the lateral processes of the preceding appendages, and ends 

 distally in a thick tubercle (Vs), which lacks gill filaments, but is 

 armed on its terminal surface with a pair of large, curved claws (d). 

 The appendage is traversed by a strong retractor muscle (F, rvs) 

 taking its origin on the dorsum of the tenth segment, and having 

 its insertion on the distal wall of the tubercle at the posterior ends 

 of the long bases of the claws (e). The resemblance in structure 

 and mechanism of these appendages to the " anal " legs of caterpillars 

 is so striking that it is difficult to believe the likeness is fortuitous. 

 The terminal body segment is better developed in the Corydalus larva 

 (fig. 36 B, X) than in Cha^diodes (fig. 35 E), in which its dorsal 

 part is rudimentary. 



Lateral appendicular processes of the abdomen, similar in every 

 respect to those of the sialid larvae, are present also on certain aquatic 

 coleopterous larvae, especially in the families Dytiscidae and Gyrin- 

 idae. In the gyrinid Dincutes, for example, the larva is provided with 

 long, tapering processes arising from lateral lobes of the body wall 

 on each side of each of the first eight segments, and with a pair of 

 two-branched processes on the ninth segment. Each process is pene- 

 trated by a trachea from the lateral respiratory trunk, and is fur- 

 nished with two short, antagonistic muscles arising in the supporting 

 lobe of the body and inserted on its base. The larva of the dytiscid 

 Coptotomns has the same equipment of lateral processes, but the writer 

 did not find muscles connected with them in a specimen examined. 



THE ABDOMINAL LEGS OF LEPIDOPTEROUS LARVAE 



A typical abdominal leg of a caterpillar consists of three parts 

 (fig. 37 A). At the base is a ring of flexible integument {mh) ; be- 

 yond this is a longer, cylindrical section {Cx) forming the greater part 

 of the appendage, and frequently having a sclerotic plate in its outer 

 6 



