24 BULLETIN 329, U. S. DEPARTMENT OF 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, 
and all hooks on the ventral surface are turned anteriorly. The 
whole operation of pupation and of spinning the pupal case takes 
from 45 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. 
The pupae of S. hracteatum and S. jenningsi have not been pre- 
viously described, and the following descriptions are given: 
DESCKIPTION OF PUPA OF SIMULIUM JENNINGSI. 
The pupa of 8. jenningsi (PI. V, fig. 4) is not more than 2.5 mm. in length, 
and is golden yellow when first formed. 
The 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. 
The pupae studied were reared from larvae and determined from 
adults reared from them and compared with the type. 
