176 PROCEEDINGS ENTOMOLOGICAL SOCIETY 



pupa showing through the skin. It is true that these tubular struc- 

 tures are crowded into a small space and their ends folded over or 

 coiled spirally; they can, however, be dissected out pretty readily and 

 unfolded far enough so that one can recognize the type of branching. 

 The hairs and booklets of the pupa are visible without further trouble 

 and one even discerns the rudiments of the legs, however without the 

 later coloring. The branching of the gill-tubes is constant in each 

 species and nearly always suffices for the recognition of the species. 

 When an unknown species is concerned one selects suitable pupge 

 which contain a fully or nearly mature imago, which is easily recog- 

 nized. One can then again dissect these out and use them for de- 

 termination. In this manner, with sufficient patience, one obtains 

 clews which are the more valuable, as even species of which the 

 imagos are very similar are plainly distinct in the pupa stage. 



Lutz considers the gill-appendages on the thorax of the 

 pupae of the first importance in specific diagnosis. 



These consist of an outwardly closed system of branched tubes 

 which show somewhat irregular and indistinct rings or spiral threads, 

 generally to near their bases, on account of which they somewhat re- 

 mind one of tracheas. Only in Simulium botulibranchium, n. sp., 

 they are entirely without rings, but chagreened with the finest scale- 

 spines, like the basal portion of the other species; nevertheless they 

 also are branched, but their entire form is so distinct and apparently 

 irregular that they are comparable with no other species. 



In all the other species examined by Lutz the number and 

 arrangement of the branches was found to be a constant and 

 reliable character. Among hundreds of pupae he found only 

 one in which a branch was obsolete on one side, and this he con- 

 sidered an abnormality. Only when the number of branches 

 reaches near twenty is there some fluctuation, and more- 

 over counting them then becomes difficult. Lutz discusses at 

 some length the various details of structure of these append- 

 ages and their range of variation. As of minor significance 

 he calls attention to the numerous spines and hooks upon the 

 abdomen. He thinks that a terminal pair of hooks which is 

 present in some species may prove important. Anteriorly there 

 are small discs covered with hair-like structures which he calls 

 trichomes. These hairs are rarely simple or dichotomous; 

 more frequently they are many-branched, and their structure 

 is of some value. Many of the pupal characters can be made 

 out even more satisfactorily on the empty pupa skin, which 

 remains uninjured within the cocoon for a considerable time. 

 Lutz finds that even the cocoons present a variety of types 

 which are characteristic of species or group of species. 



