186 ' THE UNIVERSITY SCIENCE BULLETIN. 



nymphs are clear white, with red eyes as seen from above. The limbs 

 are transparent as is the abdomen also. The antennae, claws and hairs 

 are dark. In ten minutes the limbs begin to get smoky. When they have 

 hatched within the water the guard hairs of the abdomen hang limp. 

 The insect seems water-logged. It comes up to the surface head up, and 

 repeatedly sinks back to the bottom exhausted. Finally a stronger effort 

 than before enables it to hook the front claws into the film, then after 

 a sudden turn it goes down with an air bubble imprisoned beneath the 

 abdominal guard hairs. 



In a battery jar the adults were active for a long time. The adults 

 liked to cling beneath the rubbish and Moneywort tangle. They were 

 fed the nymphs of damsel flies and Corixids. On June 25 the eggs were 

 present in all stages from those showing red eye spots to those newly 

 laid. The last of the three backswimmers was alive and active July 9 

 and the notes fail to show her fate. 



This account shows that the egg laying can be carried out under 

 laboratory conditions and that it lasts from early May to the end of 

 June at least. 



Fecundity. On March 26 a female was dissected and found to con- 

 tain 252 ova, several of which were nearly ready for laying. The period 

 of oviposition lasts from early spring until into June, in the laboratory 

 not more than a half-dozen eggs being laid on any one date. 



Longevity. Adults certainly are capable of living at least a year. 

 There is evidence to indicate that adults of the previous year may oc- 

 casionally live over until the new generation comes on in July. They 

 are few, however. If cared for in the laboratory they might exist well 

 through the second season. 



Food Habits. Like others of their kind, they are predators. In their 

 first stages in the laboratory they were given Ostracods and other small 

 Entomostraca, also Corixid nymphs. By the time they reach the third 

 instar they can master adult corixids of Palmocorixa genus (when they 

 can catch them.) As elsewhere noted, the adults show discrimination. 

 They caught but immediately liberated some pink Phyllopods offered 

 them. 



Behavior. The late instars are given to spending considerable time at 

 the surface, like the N. undulata. The adults, however, are not so in 

 evidence and come out in the sweepings of the net as pleasant surprises 

 to add zest to the activity of the amateur collector. 



Description of Stages. 

 Egg. 

 Size. Newly-laid egg, length, 1.51 mm.; diameter, .572 mm. 

 Shape. Elongate oval, but shorter in proportion to its length than N. 

 variabilis, N. undulata or N. insulata. In lateral view the anterior end of 

 the egg is seen to slope back from the base of the micropyle more than 

 the others. (See pi. XIX, fig. 6.) It is this portion of the egg that is 

 exposed as it lies in the plant stem. 



* Frisch, 1728, said that the young stages of N. glaiica were more often seen than 

 the adults. 



