( cxxvii ) 



superficially, tlie sedoeagus ; it almost always emanates from 

 a short sac, often not half its length, and it bears with it 

 paired apophyses, which are not infrequently elaborated into 

 complicated and beautiful structures, sometimes comb-like or 

 brush-like, or again they may be merely long-pointed stylets. 

 In very many genera the ninth abdominal segment is per- 

 fectly obvious, and it is interesting to observe that the develop- 

 ment of the first tergite is very considerable ; I have not yet 

 discovered any appreciable development of the first sternite 

 in any orders that have yet come under my notice. The 

 genitalia, generally speaking, vary very considerably in the 

 different genera, though the genera appear to run true to their 

 own form of structure ; for instance, in Rhyacophila the 

 harpagones or (in McLachlan's terms) the inferior appendages 

 are large, as also in Philopotamus, whilst the tegumen or superior 

 appendage is small ; whereas in Lim,nophilus the tegumen is 

 large and the harpagones are insignificant. In some genera 

 the structure is very complicated, in others equally simple. 

 I have found it a difficult task to make a selection of genera 

 whereby comparison could be made with those of the Lepido- 

 ptera, but the few I give are quite fairly representative, and 

 will, I hope, demonstrate some general idea of the similarity 

 obtaining in the two orders. 



Rhyacophila dorsalis, Curtis. 



The ninth abdominal segment forms the large and promi- 

 nent organ quite homologous to the cingula in Lepidoptera ; 

 it is a perfect collar, narrow on the venter, but widening out 

 very rapidly laterally, and ascending thus to the dorsum or 

 tegumen, where it projects forwards in a sort of saddle-shaped 

 process entirely protecting the dorsal portion of the tergite 

 armature of the anus ; this armature, forming in Lepidoptera 

 a portion of the tegumen, consists of a bifid, horn-like uncal 

 extremity, connected by narrow short laterals with a process 

 (somewhat analogous to what I take to be the gnathos of 

 Pierce) consisting of asciate-shaped horizontal sclerites, the 

 handle part being the fore extremity; below these lie the 

 very large harpagones, which are each composed of two broad, 

 slightly curved plates of chitin, articulated together, the 



