lOO SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL, 85 



cliopterous appendage, however, may be the Hmb basis of a more 

 typical abdominal appendage, while the apical claw (d) and the asso- 

 ciated middle plate (c) may possibly represent the stylus. Judging 

 from the structure there is little probability that the trichopterous 

 claw is homologous with the claws of Corydalus or Chauliodes, or 

 with the crochets of lepidopterous larvae. The lack of similarity 

 in the larval abdominal appendages of Trichoptera and Lepidoptera 

 is somewhat surprising, considering the many other structural like- 

 nesses between these two orders. 



Many trichopterous larvae are provided with a group of slender 

 processes protractile through the anus (fig. 41 F, ip), which arise 

 from the intestinal wall. In the species of Hydropsyche figured there 

 are from four to six of these processes. The structures are hollow, 

 thin- walled tubules containing no tracheae, and are therefore usually 

 termed "blood gills"; but the idea of their respiratory nature is 

 based on their structure and on the fact that they can be entirely 

 exposed by protraction through the anus, for no one apparently 

 has made any physiological experiments on their function. According 

 to Branch (1922) the organs arise as diverticula of the intestinal 

 wall produced posteriorly from the six folds of the pre-rectal part of 

 the proctodeum, and each is provided with a three-branched muscle 

 taking its origin on the intersegmental membrane between segments 

 VIII and IX of the abdomen, and extending through the lumen to 

 the tip of the processes. When retracted the processes lie in the rec- 

 tum with only their extremities exposed in the anal aperture,. Pro- 

 traction evidently is accomplished by internal pressure resulting from 

 a contraction of the abdominal walls. 



Nenroptera. — The pygidial appendages in the larvae of the sialid 

 genera Chauliodes and Corydalus, as already noted, are long, thick 

 structures projecting posteriorly and ventrally from the terminal 

 segment of the abdomen (fig. 35 D, E, Pp, fig. 36 B, E). Each organ 

 consists of a large basis (fig, 36 E, LB), supporting laterally a flex- 

 ible, tapering process representing the stylus (Sty), and bearing dis- 

 tally a short, cylindrical lobe (Vs) armed with two strong claws (d). 

 The appendage has a striking resemblance to the typical abdominal 

 leg of a caterpillar, except that the latter has no representative of the 

 stylus. The distal lobe, which clearly is serially homologous with 

 the gill-bearing tubercles of the preceding appendages in Corydalus 

 (fig, 36 B, C, D, Vs), is remarkably like the planta of the caterpillar's 

 leg (fig. T,y D, Vs). It is retracted by a strong muscle (fig. 36 F, rvs) 

 arising on the dorsal wall of the terminal body segment, and inserted 

 on the distal wall of the lobe at the posterior or upper end of the long 



