222 THE UNIVERSITY SCIENCE BULLETIN. 
creek. Since this Bool’s Backwater was surveyed nearly every day 
from earliest spring to near the end of the season, the field notes taken 
in that connection afford a splendid outline for the development of this 
species in nature. 
It would appear that this boatman prefers permanent and quiet but 
fresh waters, perhaps best suited to its needs if some part of the body 
of water has depth. Along the shores of Beebe lake, only a few hundred 
yards distant from Bool’s Backwater, a large form of this same species 
was found. The two bodies of water are connected by Fall creek, and 
the presence of two very distinct sizes seems remarkable. The larger 
form was never taken in Bool’s Backwater, but a very few of the 
smaller form were taken in Beebe lake, along with the much more 
abundant large variety. Aside from the decided differences in size, the 
females are much alike. The males, however, present differences in the 
arrangement of the palar pegs and in the strigil and abdominal segments. 
From the material examined, it would seem that the pegs of the smaller 
form show a greater tendency to crowd out of line, thus forming two lines 
at one or both ends of the series. The smaller species has a larger, 
coarser strigil than the other, while the right lateral margin of the 
abdominal segments are more spinously produced in the larger form. 
These points are figured on plate XX VII, which see. 
Life Cycle in Nature. 
Overwintering nymphs were so abundant in Bool’s Backwater and 
other species so rare that it was determined to follow the development 
of this unusual Corixid in this way. Collecting in early April brought 
forth only fourth instar forms. April 18, while the waters were still 
quite cold, the A. alternata present were mating and the P. buenoi were 
still in their overwintering stage. There was no change in matters until 
May 2, when a few in the fifth instar were taken. A count of one catch 
showed 73 per cent still in the fourth instar. It was on this date I 
noticed the May fly nymphs, which I have called the “scooter.” This 
nymph is mottled, with about the same shades as a Corixid nymph, and 
is fully as inconspicuous. They occupy the same foraging grounds, and 
it is the protective resemblance and agility in both that insure their 
perpetuity in the world. On May 9 adults of A. alternata and the over- 
wintering nymphs were notably “mited.’”’ A collection of the A. alternata 
showed 85 per cent of them to carry the water mites. By May 19 most of 
the nymphs were in the fifth instar. May 21, 97 per cent of the catch 
were in fifth instar. In a count of 300 nymphs, only one per cent of them 
were infested with mites, and in this case only one mite on each. Those 
infested with mites were delayed in molting. June 4 was a fine, warm 
day, following two or three before it, and the first adults of the P. buenoi 
were taken. There were 95 per cent still in the fifth instar. The first 
instar nymphs of A. alternata were taken on this date, which indicates 
the ease with which the overwintering species could be followed up to 
this time. Most of the adults of P. bwenoi were new fledged, as indicated 
by the softness of their integument. In fact, some were creamy yellow, 
showing that transformation had just taken place. Another item of 
