AQUATIC I.VSBCTS 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-blacky 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 breakin'g the shell. The length of pupal life is from 

 16^ 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 difSculty vfill 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 



