440 
NORTH AMERICAN PLECOPTERA 
In commenting on Barnston’s observation of the adults dip- 
ping to the surface of the water, he suggested that the insect 
might be diving in search of food, or the female descending below 
the surface to deposit her eggs. 
In 1873, Gerstaecker pointed out that Newport would have 
seen the fallacy of all such hypotheses had he observed any of 
the adults of the usual type, without gills, because they all have 
the same habit of staying in the region of streams and avoiding 
sunlight. As for dipping to the surface of the water, it could not 
be for the purpose of getting food, because, as Pictet noted, the 
reduction in the mandibles of adult stone-flies indicates that no 
nourishment is taken in that stage, but the explanation lies in 
the fact that the females dip to the water to lay their eggs. 
Gerstaecker, and a few years later Hagen, came to the conclusion 
which we still hold, that the tracheal gills of the adult are not 
essential for its existence, they are simply carried over from the 
nymphal stage, that the adults have the usual aerial method of 
respiration, being provided with spiracles as well as tracheal 
gills. 
Hagen made some further observations on this genus, espe- 
cially on the mating habits. By keeping a few adults of Pt. 
dorsata (regalis) confined in a large dish he discovered that mating 
occurred frequently, lasting each time from a quarter to half an 
hour. The male rested on the female grasping her wings with 
his feet, then bending the end of the abdomen under that of the 
female and using the dorsal appendages (that is, the two lobes 
of the bifid tenth tergite) to open up the genital passage, he 
quickly brought the penis forward into the vagina. The penis 
being separated from the opening of the sperm duct by the 
anus, functioned as a sperm-conveyer. Actual egg-laying was 
not witnessed, but masses of yellow-green eggs were found on the 
grass or in the water in the bottom of the dish. In two or three 
days the egg showed segmentation, but the water was evidently 
too warm for development to continue. 
Ny7nph. There are scarcely any biological data on the nymph. 
Barnston observed that it constantly resided in the water “at 
the botton of streams and rivers.” I have always found it cling- 
ing to the under side of stones in the most rapid parts of streams. 
