HUNGERFORD: AQUATIC HEMIPTERA. 193 



legs may serve as an illustration of this point. In all the instars the 

 tarsi end in unequal claws as in the adult, and the tibiae possess a 

 row of five bristles on their caudo-ventral margin and the tarsi three 

 such bristles. 



The metathoracic tarsi end in an unequal pair of claws which are 

 prominent in the first instar (plate XX, figure 10), and which become 

 less and less conspicuous as development proceeds till in the adult 

 stage their similarity to the other structures of the swimming leg has 

 led to the common statement that the tarsal claws of hind legs are ab- 

 sent in the adult. Upon transforming to the adult stage the 1-segmented 

 condition of the tarsi is replaced by a 2-segmented tarsus and the 3- 

 segmented antennae become 4-segmented. (See plate XX, figures 6 

 and 7.) 



The eyes occupy an increasingly large proportion of the head in 

 successive instars, a point not properly indicated in the drawings which 

 were made from living bugs in the water. 



Summary. Notonecta undiilata is the most widely distributed of all 

 our backswimmers. It lives well in the aquarium and may be reared 

 from deposition of the egg to the adult stage in some forty days if 

 placed in isolated jars and given proper attention. The young stages 

 thrive on a diet of Ostracods and the advanced nymphs do very well on 

 immature and small Corixids for a food supply. In Kansas there are 

 two main broods in a season, one reaching the adult stage in June, the 

 other in August. Since these insects draw quite largely in their young 

 stages upon the Ostracods and similar organisms, which represent a 

 chief food supply for young fish, as well as preying upon a small fish 

 directly, as has been noted several times, they deserve more careful 

 study. This task is greatly facilitated by a workable key to the species 

 and by some knowledge of their feeding habits. 



Biology of Notonecta. Variabilis. 



This species was very abundant in the pools about the Field Station, 

 Ithaca, N. Y. The writer has never taken it in Kansas, although it 

 should occur there. It likes fresh water, and clings to submerged 

 tangles of water plants. 



The Egg. 



The egg is deposited upon a pad of gelatinous material. This 

 egg appears to be more truncate at anterior end than the other eggs. 



Size. Length, 1.69 mm.; width, top view, .65 mm.; width, side view 

 ( heigh th), .78 mm. 



Color. Surface is hexagonally reticulate; pearly white when first de- 

 posited, then turns first amber and then smoky as embryo develops, 

 especially at anterior end. Micropyle tube is long and directed toward 

 attached side of egg. 



Shape. As in other species. 



First Instar. 



Size. Length, 2.08 mm.; width of body, .936 mm.; width of head, 

 .78 mm. 



l.-i — Sci. Bui. — 1669. 



