194 HYDROCORI9.E, OR WATER-BUGS. 



from the imago in their smaller size, and in the deficiency of 

 wings. When they descend into the water, the Notonectidae 

 carry down a supply of air for respiration, in a hollow which 

 exists beneath the wings, when these are folded together. The 

 NEPID^E, or Water- Scorpions, receive their name from the scor- 

 pion-like form of their fore-legs, which are efficient instruments 

 for seizing their prey. They are in most respects similar in 

 structure and habits to the insects of the preceding family ; but 

 their motions are much slower, their legs not being so advantage- 

 ously formed for swimming. The species represented in the ac- 

 companying figure is a very common inhabitant of our ponds. 







