The South Australian Naturalist. 127 



as it to make stire that the operation has been sttccessfnl. The 

 female then swims away, vigorously cleaning the ovipositor 

 from particles of plant tissue with the hind legs ; the whole 

 operation of boring the hole and depositing the o^'um occupies 

 about one minute. AVhile egg-laying is in progress the males 

 seem greatly excited, stridulating continually, and following 

 the females around the aquarium. 



At least two generations occur every summer ; the period 

 of incubation for the eggs varies according to the temperature' 

 of the water and the time of the year. Those we are discuss- 

 ing were laid in early spring, and take about three weeks to 

 hatch. A fortnight after dej^osition the first external indica- 

 tion of the enclosed embryo is apparent, tAvo smudges of red 

 pigineut appearing near the apex of the egg; these bodies are 

 the developing eyes of the little bug as seen through the semi- 

 ti'anspai'ent chitin of the egg-shell. The patches become more 

 l^rominont, and in a few days, when the nymph is almost ready 

 to hatcli, they have assumed a kidney-like shape and are dark 

 red in color. In hatching, the nymph bursts open the top end 

 of the egg-shell and struggles out head first ; the little fellow 

 resembles in general the adult, but is, of course, very tiny, 

 being less than 2 mm. in total length. The most striking 

 differences are that all the tarsi are one-jointed with much 

 longei- claAvs than in the imago, the venter lacks the abdomi- 

 nal gutters, the eyes are small and widely separated, and there 

 are no traces of Avings. As the nymph hatches l)elow the 

 surface, the guai'd hairs immediately after emergence contain 

 no trapped air, but are quite limp ; the nymph is therefore 

 not buoyant, and makes many spasmodic and unsuccessful 

 attempts to reach the surface film and so gain access to the 

 air. Several examples in this condition were isolated in a 

 small vessel, and for three days tumbled about awkwardly, 

 often sinking to the bottom dorsum uppermost — which is 

 ''wrong side up" for a back-swimmer when it is in the water; 

 During this period ''dissolved" air may have been absorbed 

 through the skin by osmotic action, for the abdominal hairs 

 held no air whatever. Once, however, that the nymph has 

 succeeded in introducing air beneath the guard hairs, it is in 

 innnediate control of its movements, poising in the water as 

 do the adults, and at once commencing to feed. As a means 

 of providing food for the youngsters egg-rafts of the Common 

 Grey Mosquito (Culex fatigans) were placed on the surface 

 of the Avater; the little bugs easily mastered the tiny mosquito 

 larvae as they emerged. The nymphs are quite as rapacious 

 as the adults, and as successive stages are attained larger 



