220 NATURAL HISTORY OF AQUATIC INSECTS CH. 



An immersion of upwards of fourteen hours, how- 

 ever, caused insensibility and apparent death. Both 

 males and females enter the water. In the same pond 

 was found a second species of similar habits, referred 

 to a new genus, Prestwichia. 



" Whereas Polynema natans swims with its wings 

 and uses its legs apparently only for walking, the 



FIG. 78. Polynema (Anaphes) natans, side-view of female, X 30. From Lubbock. 



present species (Prestwichia) when under water, holds 

 its wings motionless, and uses its legs as oars. 

 Though they are neither flattened nor provided with 

 any well-developed fringe of setae, still they seem to 

 serve their purpose pretty well, and the motion of 

 this species is more rapid than that of the former. 



