362 AN INTRODUCTION TO ENTOMOLOGY 



In most cases the eggs of corixids are attached to the stems of 

 aquatic plants; but Ramphocorixa acuminata usually attaches its 

 eggs to the body of a crayiish. 



The males of most of the Corixidse are furnished with stridulating 

 organs. These consist of one or two rows of chitinous "pegs" on the 

 fore tarsi and a roughened area on the inner surface of the fore femora 

 near the base. By rubbing the tarsal comb of one leg over the 

 roughened area of the femur of the opposite leg, a chirping sound is 

 produced. These stridulating organs differ in form in different species. 



In addition to the stridulating organs of the fore legs there is in 

 certain species a more or less currv'-comb-like organ near the lateral 

 margin of the dorsal wall of the sixth abdominal segment ; this has 

 been termed the "strigil." It is situated, when present, on the left 

 side in Corixa and on the right side in several other genera. Its func- 

 tion has not been definitely determined. 



Both the adults and the eggs of Corixa are used for food for man 

 and for birds in Mexico and in EgA-pt. The eggs are gathered from 

 water-plants. Glover states that in Mexico the natives cultivate a 

 sedge upon which the insects will deposit their eggs; this sedge is 

 made into bundles, which are floated in the water of a lake until 

 covered with eggs; the bundles are then taken out, dried, and beaten 

 over a cloth ; the eggs, being thus disengaged, are cleaned and powdered 

 into flour. Kirkaldy ('98) reports the importation into England of 

 Corixa mercenaria and its eggs for food of insectivorous birds, game, 

 fish, etc., by the ton; and computes "that each ton of the adults will 

 contain little short of 250 million individuals!! As to the ova, they 

 are beyond computation." The adults are captured at night with 

 nets when they leave the water in swarms. 



It is difficult to separate the different species of water-boatmen on 

 account of their close resemblance to each other; this is especially 

 true of the females. Fifty-five species are listed in the Van Duzee 

 check -list; these represent six genera. 



Family NOTONECTID^ 



The Back-Swimmers 



The Notonectidae differ from all other aquatic Hemiptera in the 

 fact that they always swim on their backs ; and there 

 is a corresponding difference in the form of these in- 

 sects. The body is much deeper than in the allied 

 families, and is more boat-shaped. The back, from 

 the peculiar attitude of the insect when in the water, 

 ■^^8- 416.— iVo/o- corresponds to the bottom of a boat, and is sloped 

 necta unduLata. ^^ ^^ ^^ greatly resemble in form this part (Fig. 416). 

 The eyes are large, reniform, twice sinuated on the outer side, 

 and project a little way over the front margin of the prothorax. Ocelli 

 are absent. The prothorax has the lateral margins sharp and pro- 



