AQUATIC INSECTS IN NEW YORK STATE 335 
ing larvae, and attempted to rear them, by placing them in 
aquaria of running water, but succeeded with only four speci- 
mens. The first of these cast its larval skin on May 20; the 
second on the 25th, the third on the 26th, and the fourth on the 
27th. The casting of the larval skin is most rapidly accom- 
plished. A larva in the breeding cage attracted attention be- 
cause of its grayish color, not so black as usual, the pale color 
owing, probably, to the skin being loosened. A moment later, 
perhaps half a minute, the empty larval skin was seen floating 
away, leaving the cream-white pupa on precisely the same spot 
which had been occupied but a moment before by the larva. In 
the new pupa, the constrictions of the body so distinctive in 
the larva, were still plainly visible; within half an hour they 
began to disappear, and the color gradually became darker. In 
from three to four hours the pupa had assumed its character 
istic shape, and the coal-black color. The four empty larval 
skins examined, all had a small irregular break on the ventral 
surface just cephalad of the first sucker, and another small 
T-shaped opening on the dorsal surface opposite the one on the 
ventral. The rest of the skin, including the suckers, remained 
intact. 
The pupa is coal-black, heavily chitinized, and is shaped like 
the half of a longitudinally cut egg, though somewhat more 
flattened. At the anterior end is a pair of dorsal, prothoracic 
tracheal gills, each gill consisting of four flattened plates. The 
whole of the flat ventral surface of the pupa is fastened so 
firmly to the rock that it is practically impossible to remove it 
without breaking the shell. The length of pupal life is from 
163 to 18 days. If the pupae be taken from the water on the 
piece of rock to which they are attached, removed to the 
aquaria, and placed with the heads down stream, under a small 
stream of water, no difficulty will be experienced in rearing 
them. A number of specimens reared in this way were ob- 
served by the writer to emerge. From five to 15 minutes 
are required for the imago to free its body from the pupal 
Skin, the wings remaining folded till the abdomen _ is 
