414 NEW YORK STATE MUSEUM 
trunks can easily be followed, and are seen to open at its extrem- 
ity. On each side of this tube is a single row of short spines, 
and at the base is a tuft of short hairs. On each side of the 
eighth segment is a comb composed of a variable number of. 
short spines [pl.45, fig.6]; the tip of each spine is sometimes 
covered with short hairs. 
The ninth abdominal segment, usually shorter than the others 
and of less diameter, contains the rectum and the anus, being 
almost at the extremity of the body. Around the opening are 
two pairs of delicate, elongate lobes. These are tracheal or 
blood gills. Immediately cephalad of these are dense tufts of 
long hairs, the position and arrangement of which are variable 
with the species. Usually also, dorsad of the blood gills are a 
variable number of long bristles. 
Pupa. The pupa differs from those of the other genera of 
this family less than does the larva. It is characterized by its 
bulky, oval, laterally compressed anterior part, made up of the 
head, thorax and its appendages, and a posterior part, consist- 
ing of the abdomen with its swimming paddles [p1.43, fig.7]. The 
length of ‘pupal life in all observed specimens was about four 
days. During this time the pupa would remain quietly floating 
with its thorax nearly vertical, its abdomen bent under, unless 
disturbed, when it propels itself to the bottom by means of 
the violent contractions of the abdomen, after the fashion of a 
crawfish. The specific gravity apparently being less than water, 
however, it requires a constant effort to remain at the bottom. 
>» The head is bent down under the thorax, the antennae folded 
back arcuate and lying along its sides; the legs folded up in a 
sinuate fashion; the wings extending downward and backward 
from the sides. Near the highest point of the thorax, the pupa 
occupying its usual vertical position [pl.43, fig.7], are the two 
breathing trumpets, elongate, subcylindrical tubes, open and 
somewhat flaring at the top [pl.44, fig.11]. On the dorsal surface 
near the posterior margin of the thorax, are usually a pair of stel- 
late hairs. The abdomen has eight segments, subequal in length 
except the first and last two, which are shorter, and on the pos- 
terior margins of which are a few tufts of branched hairs. 
Attached to the last segment is a pair of broad swimming pad- 
dles, each reinforced by a stout longitudinal rib, and ending in 
a single short spine. Between the paddles is a furcate fleshy 
process in which are contained the genitalia of the inclosed 
imago. The shape of this fleshy process differs with the sexes, 
and perhaps also with the species. The pupae of all the species 
I have examined resemble one another so closely that I have 
been unable to distinguish them. It appears however that there 
