Hale — Aquatic Hemiptera 409 



tliird, 6-8 days; fourth, 7-10 days, and the fifth about 10 days. Thus the nymph 

 attains maturity about two months after the egg is laid. 



Habits of the Nymphs. The newlj^-hatched nymphs, as in the case of 

 larvae of other Notonectid genera observed by Hungerford, are singularly help- 

 less until the guard hairs have become charged with air ; after tuml)ling about 

 in awkward efforts to attain the surface film, they sink to the bottom exhausted. 

 Several examples in this condition were placed in a small dish containing water 

 to the depth of half an inch, and after three days none had filled its guard hairs; 

 possibly during this period respiration was effected througJi the skin by osmotic 

 action. They Avere then placed in a "balanced" aquarium containing ample 

 weed, and next morning, with guard hairs filled, all were poised in the water, 

 active and feeding. These first instar nymphs remain quite near the surface 

 and behave much as do the imagos. In situations where Anisops is breeding, 

 they do not mingle with the more developed examples, but congregate in the 

 shallowest water at the margins of the pools, the shoals often comprising many 

 thousands of individuals; adults do not appear to prey upon these swarming 

 nymphs. 



Tlie moulting is not the least interesting phase of the metamorphosis : the 

 skin splits along the dorsal median line of the thorax (where it is weakest), but 

 the integument of the abdomen is unruptured ; the skin of the head splits at the 

 junctures of the eyes and notocephalon. The legs are drawn out of the previous 

 sheaths, leaving the last-named, complete with swimming hairs, spines, etc., 

 intact ; the abandoned skin fioats at the surface, a hollow replica of the nymph 

 from which it is practical to compute leg and other measurements. Occasionally 

 a nymph fails to rupture the skin and so dies ; in an example which has perished 

 thus the dorsum is characteristically humped owing to the abortive effort to burst 

 the skin. After each moult the bug immediately expands to the proportions of 

 the next instar. 



Developmental Changes. The first instar nymph has no ventral carina on 

 the abdomen and, even towards the end of the instar, very little pigment on the 

 venter. The claw^s, as in the adult, are unequal, but are relatively much larger, 

 decreasing regularly in proportion to the size as the bug grows; the posterior 

 claws, for in.stance, are conspicuous in the first instar nymph, and measure one- 

 fifth of the length of the tarsus, while in the adult they are small, hidden by the 

 swimming hairs, and but one-tenth of the length of the tarsus. The anterior and 

 intermediate tibiae and tarsi are concave on their inner surfaces as in the imago, 

 but all the tarsi are single-jointed until after the final moult. The width of the 

 h'.ynthlipsis in relation to that of the vertex does not differ greatly throughout the 

 life history, but the eyes are at first small and the notocephalon is proportionally 



