HEMIPTERA 361 



ture: the head overlaps the prothorax instead of being inserted in 

 that segment; the beak is very short and scarcely distinguishable 

 from the face, the opening to the mouth being on the front of the so- 

 called beak; the tarsi of the front legs (termed palce) are flattened 

 or scoop-like in form; each consists of a single segment and bears a 

 comb-like fringe of bristles; the middle legs are long, slender, and 

 end in two claws ; the hind legs are flattened and fringed for swimming ; 

 and, in the males, the abdominal sterna, especially the four caudal 

 ones, are very uns>TTLmetrical, being on one side broken into irregular- 

 shaped fragments. 



The water-boatmen have the body flattened above, and swim 

 upon their ventral surface; they differ in these respects from the 

 members of the next family. They swim with a quick, darting 

 motion ; they use for this purpose chiefly their long, oar-like, posterior 

 legs. When in their favorite attitude, they are anchored to some 

 object near the bottom of the pond or aquarium by the tips of their 

 long, slender, intermediate legs; at such times the fore legs hang 

 slightly folded, and the posterior legs are 

 stretched out horizontally at right angles to 

 the length of the body. The body of these 

 insects, with the air which clings to it, is much 

 lighter than water; consequently whenever 

 they lose hold upon the object to which they 

 have been clinging, they rise quickly to the 

 surface, unless they prevent it by swimming. 

 They occasionally float on the surface of the 

 water, and can leap into the air from the 

 water and take flight. Fig. 415.— A water-boat- 



The bodies of these insects, as they swim ™^"- 

 through the water, are almost completely 



enveloped in air. The coating of air upon the ventral surface and sides 

 can be easily seen, for it glistens like silver. By watching the insects 

 carefully when they are bending their bodies, the air can be seen to fill 

 the spaces between the head and the prothorax, and between the pro- 

 thorax and the mesothorax. The space beneath the wings is also filled 

 with air. When these insects are in impure water, they must come 

 to the surface at intervals to change this supply of air. But I have 

 demonstrated that in good water it is not necessary for them to do 

 this. The air with which the body is clothed is purified by contact 

 with the fine particles of air in the water ; so that the insect can breathe 

 its coat of air again and again indefinitely. 



It has been commonly believed that the corixids are carnivorous ; 

 but Hungerford ('19) has shown, by an extended series of experiments, 

 that these insects gather their food supply from the ooze at the 

 bottom of pools in which they live. This fiocculent material they 

 sweep into their mouths by means of the flat rakes of their fore tarsi. 

 This material is largely of plant origin; but the protozoa and other 

 minute animals living on it are also consumed. This author also 

 found that the corixids feed on the chlorophyll of Spirogyra, 



