24 THE UNIVERSITY SCIENCE BULLETIN. 
days of March found Notonectids and Corixids flying to it 
from the Smith pond. By the last of the month Corixids were 
laying eggs. April 11 there were not many adult bugs where 
they had been exceedingly abundant before. The back-swim- 
mer eggs were showing red eye spots. By May 4 the pool was 
full of activity. Ostracods were exceedingly abundant and 
Notonectids in first and second instars were preying upon 
them in numbers. Gerrids in second instar were upon the 
water and many marshtreaders were upon the floating dead 
leaves of cattail, mats of algze and sprouting masses of cattail 
seed. Corixids from the first to the fifth instar were abund- 
ant, but perhaps the larger number were in the third and 
fourth instars. A few adults were present. The tenth of 
May was a fine warm day and the Cattail pool was a great 
place to study young water-bug life. Droves of Gerrid nymphs 
and marshtreaders made the surface seem a busy place in- 
deed, while the Corixid and Notonectid nymphs were in droves 
within the water. It was May 17 before the first adults of the 
spring crop of water bugs were noted in this pool. These were 
new fledged Corixids. It was May 25 before the Gerrids and 
Notonectids attained the fifth instar in numbers, and at this 
time a new bug was dominant upon the floating vegetation 
of the pool. This was the new adult generation of Mesovelia 
mulsanti, and the presence of large numbers of these silvery- 
winged forms brought them at once to the attention as they 
moved about over the green alge. The green nymphs had at- 
tracted little attention in the same situation a few days be- 
fore. On May 28 most of the Corixids were adult and the 
pool was roily from a recent rain. The young Marshtreaders 
were out in force upon this date, and were rivals of the Meso- 
velias for prey. May 30 the Gerrids were transforming, and 
the next day the first back-swimmers were seen to emerge into 
the adult state, yet there were nymphs from first instar up. 
On the morning of June 3, the notes show that the cattails 
were in bloom and young plants were encroaching upon the 
clear water space very steadily. From this day’s record and 
a comparison of the notes of other days regarding the appear- 
ance of the stages of the water insects, one is impressed by the 
remarkable synchronism of development, not only of the water 
bugs, but hand in hand with them, of the water beetles. And 
here we find the flowering of the cattail heralding the advent of 
