182 THE UNIVERSITY SCIENCE BULLETIN. 



helpless nymph caught by a hungry neighbor while disengaging himself 

 from the integument of an abandoned instar. Other water bugs of his 

 size and larger, with predatory tendencies, water beetles, etc., are his 

 enemies. Needham figures a nymphal dragon fly in the process of de- 

 vouring an unfortunate back-swimmer. In the matter of parasites, he is 

 burdened with the usual Hydrachnid mites, and a tiny wasp parasitizes 

 its eggs 



From the larger forms of life the back-swimmers enjoy considerable 

 measure of immunity. Seldom, indeed, have they been taken in the 

 stomach contents of fishes and the like. Little wonder that they are a 

 dominant form of pond life. The abundance of back-swimmers and 

 boatmen in the same pool has been difficult to understand until recent 

 investigations into the habits of these two types have cleared up the 

 question. 



Notonecta insulata. 

 This large back-swimmer compares favorably with N. irrorata in size, 

 yet even its largest varieties could be distinguished readily from the latter 

 by the marked differences that exist in the shape of their heads and 

 bodies. This fellow was less common at Ithaca than N. irrorata. It re- 

 mains much submerged and this may account for the infrequency with 

 which it was captured. On April 29, two mating pairs were taken in 

 the west pool of Ringwood Hollow. They were brought to the laboratory, 

 and when placed in a battery jar, mated again. They remained in copula 

 as long as the observation was continued — a half hour or more. Since 

 Hagemann, according to Wefelsheild, reports Corixa remaining in copula 

 1 to 2 days, and from our experience with other water bugs, we would 

 not be surprised at a long duration for the process in this bug. 



During the day, April 30, 14 eggs were laid — large, white eggs, at- 

 tached to the stems. These eggs are considerably larger than those of 

 N. irrorata. Thirty eggs were present May 4. One of the males died 

 May 6 and was pinned up. On May 10 there were 26 more eggs. Thus in 

 the first twenty-four hours the two females averaged 7 eggs apiece, this 

 average falling off somewhat later. On May 9 a few of the eggs were 

 showing pink eye spots. Some of these were photographed and are shown 

 on plate VIII. May 19 many of the eggs showed very dark red eye spots 

 and gave evidences of hatching shortly. The first hatched on May 23. A 

 careful study of these newly hatched was disappointing in a way. In- 

 stead of coming to surface, they remained submerged. The newly hatched 

 are white with transparent abdomen and limbs. The guard hairs of the 

 abdomen hang limp. Two little fellows hatched at 1:10 p. m. They were 

 active ten minutes later, making series of backward somersaults, then 

 resting as though exhausted. All efforts appear to be to attain the sur- 

 face film, but at 2 :20 they were still unsuccessful, and when resting on 

 the bottom of the jar were indifferent as to which side was up, back or 

 venter. Five o'clock came and still they were below, the guard hairs 

 hanging limp upon the venter. Finally the next day some fresh water 

 was added and some bubbles left upon the surface. Into these I coaxed 

 one nymph, with the result that it filled its guard hairs instantly and 

 darted below! This fellow was transformed of a sudden into a very ac- 



