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 algae 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 algae. 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 



