24 BULLETIN" 329, U. S. DEPARTMENT OP AGRICULTURE. 



strong hooks on the dorsal and ventral surfaces of the abdomen. 

 These hooks are turned anteriorly on the dorsal surface on segments 

 2, 3, and 4 ; posteriorly on the dorsal surface of segments 7, 8, and 9, 

 arid all hooks on the ventral surface are turned anteriorly. The 

 whole operation of pupation and of spinning the pupal case takes 

 from 48 minutes to 1 hour. 



GENERAL DESCRIPTION. 



The pupae of Simulium at first are generally golden yellow or light 

 brown, the color and shape of the adult organs showing very clearly 

 through the pupal skin as the time of emergence approaches. There 

 are nine abdominal segments. On each side of the thorax are situ- 

 ated the respiratory organs, composed of long chitinous tubes, aris- 

 ing from a main stalk, tapering somewhat, and usually branching 

 dichotomously toward the distal end. The number of filaments, 

 always, counting the branches of the distal ends, varies according to 

 the species, from 4 to 60, and is an excellent systematic character, 

 as it is very constant for each species. On the dorsal and ventral 

 surfaces of the abdomen are situated rows of strong chitinous hooks. 

 These seem to be of little use as distinguishing characters for the 

 five species discussed in this paper, as they are approximately the 

 same in number and have about the same position in each. The 

 pupae can be positively correlated with the adults by the dissection of 

 mature male pupae and study of the genitalia. 



iThe pupse of S. bractecutum and S. jenningsi have not been pre- 

 viously described, and the following descriptions are given : 



DESCRIPTION OF PUPA OF SIMULIUM JENNINGSI. 



The pupa of &. jenningsi (PI. V, fig. 4) is not more than 2.5 mm. in length, 

 and is golden yellow when first formed. 



IThe respiratory filaments, which are situated at each side of the thorax near 

 the head, are each composed of a single main trunk, which divides at base into 

 the following branches : Four single unbranched filaments and two long fila- 

 ments, each of which divides again dichotomously, making eight branches in 

 all, counting the distal ends of the branches. 



: On the dorsal surface of the abdomen there is a row of very small hooks on 

 each side of the second segment, and on the third and fourth segments rows of 

 four very large hooks on each side pointing cephalad. On the fifth segment 

 there is a row of hooks pointing caudad, and on the ninth segment a row of 

 minute hooks near the cephalic margin and a single large hook on each side 

 at the middle of the segment. On the ventral surface of the abdomen there 

 are two large hooks close together on the fifth segment, and two large hooks, 

 rather far apart, on each of the sixth and^ seventh segments. The caudal end 

 of the pupa is cleft for a short distance in the middle. 



I The pupae studied were reared from larvae and determined from 

 adults reared from them and compared with the type. 



