HEMIPTERA 363 



jecting. The legs are all long ; the hind pair are much the longest and 

 fitted for swimming. The tarsi consist each of three segments, but 

 the basal segment is so small that it is often overlooked. There is a 

 ridge along the middle line of the venter which is clothed with hairs, 

 and along each side of this a furrow. Along the upper edge of the 

 outside of this furrow and a short distance from the side of the body, 

 there is a fringe of long hairs, and beneath this fringe the abdominal 

 spiracles are situated. 



The features presented by the ventral side of the abdomen just 

 referred to can be seen on dead specimens; but it is well to examine 

 them on living insects. This can be done by placing a back-swimmer 

 in a glass of water, and, when it is resting at the surface of the water, 

 studying it by means of a lens of low power. Under these conditions 

 it can be seen that the furrow on either side of the venter is an air- 

 chamber, which is enclosed by the two fringes of hairs, one borne 

 by the ridge of the middle line on the body and the other by the 

 outer margin of the furrow. It can also be seen that there is a hole 

 near the tip of the abdomen through which the air passes into the 

 chambers beneath the fringes of hairs. Sometimes when watching 

 an individual under these conditions it will be seen to force the air 

 out of the chambers beneath the fringes of hair, using the hind legs 

 for this purpose, and sometimes an entire fringe will be lifted like a lid. 



By examining the first ventral abdominal segment of a dead indi- 

 vidual a little furrow can be seen on each side; these are air-passages 

 extending between the chambers on the ventral side of the abdomen 

 to that beneath the wings. 



Air is also carried among the hairs on the lower side of the thorax, 

 and in the spaces between the head and the prothorax and between the 

 prothorax and the mesothorax; this is probably expired air. 



In collecting back-swimmers, care must be taken or they will inflict 

 painful stings with the stylets of their beak. 



The manner of oviposition of these insects differs in different spe- 

 cies. Some merely attach their eggs to the surface of aquatic plants 

 by means of acolorless, water-proof glue; others have a long oviposi- 

 tor by means of which they insert their eggs in the tissue of these 

 plants. 



The males of some back-swimmers possess stridulating areas; 

 these are located on the femora and tibiae of the fore legs and on the 

 sides of the face at the base of the beak. 



The notonectids of our fauna represent three genera ; these can be 

 separated by the following table : 



A. Legs dissimilar; hind legs flattened and fringed for swimminfr. 



B. Last segment of the antennas much shorter than the penultimate segment. 



NOTONECTA 



BB. Last segment of the antennae longer than the penultimate segment. 



BUENOA 



AA. Legs quite similar Plea 



Noionecta. — To this genus belong the greater number of our 

 species, of which twelve have been described. These are the back- 



