NATURAL HISTORY. 39 
and the smaller one the Notonecta striata, both 
magnified. 
The body of this insect is fringed with long 
hair, and on each side, and down the middle of 
the abdomen, are disposed thick rows of the 
same. In the larger species they are very per- 
ceptible; their office appears to be that of buoy- 
ing the insect on the surface of the water with- 
out requiring any muscular exertion, which is 
performed in this manner:—The insect rises to 
the surface, and elevates the inferior extremity 
of the body; then lifting up the side rows of 
hair, it permits a portion of air to enter the 
channel which they previously occupied, and 
there retains it. When it wishes to sink, I ob- 
serve that it strokes down the fringe with the 
feet, and thus liberates the air, by which means, 
