TRANSFORMATIONS OF BUFFALO GNATS. 



13 



quire swiftly flowing water for their development. The full-grown 



larva of the largest species, according to Johannsen, measures not 



more than 15 mm. in length. The American species 



known to the writer measure from 12 mm. (S. pic- 



tipes) to 3.5 mm. (S. jenningsi). The larvae are 



generally subcylindrical, somewhat attenuated at the 



middle, and with a gradual dilation toward the anal 



extremity. In addition to the head there are 12 



rather indistinct body segments. 



In -the larval stage the shape and number of the 

 branches of the rectal gills seem to be good sys- 

 tematic characters, not differing essentially among 

 individuals of the same species. If the number and 



length of the an- 

 tennal joints, the 

 teeth in the 

 mentum, and the 

 character of the 

 dorsal markings fig. 3 

 of the head are 

 also used, the de- 

 termination of 

 half-grown 

 larvae is possible 

 in their last stage can be corre- 

 lated positively with their re- 

 spective pupae by the dissection and study of the pupal filaments, 

 which become fully developed under the larval skin. 



As the larvae of 8. bracteatum and S. jenningsi have not been pre- 

 viously described, the follow- 

 ing descriptions are given. 



DESCRIPTION OF LAEVA OF SIMULIUM 

 BKACTEATUM. 



The full-grown larva is from 6 

 to 6.5 mm. in length. The general 

 color varies from light yellowish- 

 brown to grayish, with conspicuous 

 brownish markings on the ventral 

 surface. The antennse (fig. 3) are 

 slender, 4-segmentecl ; * the second 

 segment one and one-half times as 

 long as the first ; the third segment as long as the first ; the fourth a short 

 conical process ; the general color pale hyaline ; the first segment infuscate. 



The labial plate (fig. 4) is more strongly serrate than that of S. rcmistum 

 (fig. 5) : the apical margin rather convex; the middle tooth and each corner 

 tooth very large. There are from four to five long bristles near the lateral mar- 

 gin on each side. 



Fig. 4. — Simulium bracteatum. 

 larva. Greatly enlarged. 



Labial plate of 

 (Original.) 



Simulium 

 tracteatu m . 

 Antenna of 

 larva. Greatly 

 enlarged. (Orig- 

 inal.) 



The larvae 



Fig 



-Simulium venustum. Labial plate of 

 larva. Greatly enlarged. (Original.) 



1 The writer differs from other writers in regard to the segmentation of the antennse. 



