']Qi IMOTIO.NS or INSECTS. 



the whirl wig- {Gi/rinus) — so as to resemble the paddle 

 of an oar. When the Dytisci rise to the surface to 

 t^ke in fresh air — a silver bubble of which may often 

 be seen suspended at their anus — they ascend, as it 

 should seem, merely in consequence of their being spe- 

 cifically lighter than the water ; but when they descend 

 or move horizontally, which they do with considerable 

 rapidity, it is by regular and successive strokes of their 

 swimming legs. While they remain suspended at the 

 surface, these legs are extended so as to form a right 

 angle with their body. The JSotoncctce swim upon their 

 back, which enables them to see readily and seize the 

 insects that fall upon the water, which are their prey. 

 Sigarciy however, a cognate genus separated from No- 

 tnnecta by Fabricius, swims in the ordinary way. As 

 the Gyrini are usually in motion at the surface, whirl- 

 ing round and round in circles, it is probable that their 

 legs are best adapted to this movement. They dive 

 down, however, with great ease and velocity when 

 alarmed. The common water-bug (Gerris lacustris, 

 Latr.), though it never goes under water, will some- 

 times swim upon the surface, \vhich it does by strokes 

 of the intermediate and posterior legs^. These, how- 

 ever, are neither fringed nor dilated, but very long and 

 slender, with claws, not easily detected, situated un- 

 der the apex of the last joint of the foot, which covers 

 and conceals them. The underside of their body — as 

 is the case with Elophorus, F., and many other aquatic 

 insects — is clothed with a thick coat of gray hairs like 

 satin, which in certain lights have no small degree of 

 lustre, and protect its body from the effects of the water. 



^ De Geer,iii.314. 



