TRANSFORMATIONS OF BUFFALO GNATS. 



15 



The rectal gills (PL IV, fig. 5) are three-branched, each lateral branch bear- 

 ing six lobes and the middle branch five, as a rule. This is a smaller number 

 of lobes than is found in vcnustum (PL IV, fig. 9), which 

 has seven or eight on each lateral branch. 



The caudal sucker bears from 70 to 75 rows of hooks. 



The larvae were taken by the writer from a fair- 

 sized stream near Spartanburg, S. C, in August. 

 1913, and were separated from the larvae of other 

 species by the number of branches of the pupal 

 filaments (formed underneath the larval skin) and 

 determined from adults reared from them and com- 

 pared with the type. 



EXTERNAL AND INTERNAL STRUCTURES OF THE LARViE. 



The head is more or less quadrangular in shape 



and very chitinous. The eyes have become reduced 



to mere pigment cells, in the shape of two irregular 



black blotches, situated on each side of the head. 

 In addition to the usual mouth parts, the head 



bears a pair of peculiar fan-like organs, situated 



one on each side at the anterior end. The rays or 

 cilia of the fans are attached at 

 the base each by a strong peduncle 

 and range in number from 30 to 

 60 according to the species. On 

 the inner margin of these cilia are 

 fringes of short hairs interspersed with minute 

 teeth. As the number of cilia varies in individuals 

 of the same species, they are not very reliable 

 specific characters. The fans, acting as strainers, 

 catch the microorganisms on which the larvae feed 

 and sweep them into the mouth. 



The antennae (figs. 3, 7, 8, 10, 11) are situated at 

 the sides of the head, on the dorsal surface toward 

 the cephalic end, just below the base of the fans. 

 They are slender, and in the species examined, 

 naked. Johannsen says "The antennae are appar- 

 ently jointed * * * the first joint twice as 

 long as the others taken together; the second, 

 slender cylindric * * * the third joint a short 

 pointed process at the apex of the second." Miall 

 says "Small three- jointed antennae" and gives a 

 figure in which the antennae have three long joints 



and lack the short pointed process forming the last joint. Of 



the five species dealt with in this paper, the larvae of Simulium 



venustum (fig. 8), S. pictipes (fig. 10), and S. hracteatum (fig. 3) 



Fig. 10. — Simulium 

 pictipes. An- 

 tenna of larva. 

 Greatly e n - 

 larged. ( Orig- 

 inal.) 



Fig. 11. — Simulium 

 v it tat u m . An- 

 tenna of larva. 

 Greatly en- 

 larged. ( Orig- 

 inal.) 



