2030 



The Cornell Reading Courses 



an abundance of vegetation. Among the Crustacea there are the fresh- 

 water sow bug, Asellus, and the fresh-water shrimps, Hyalella, Gam- 

 marus, and Eucrangonyx. These may be obtained from almost any 

 swamp or marsh .having permanent pools containing vegetation. If 

 the plants are pulled up by the roots and rinsed in a bucket of water, 

 the animals will fall off into the water. 



Nearly all of the fresh-water snails and small clams, Sphaerium, are 

 relished by many pond fishes. The forms illustrated in figure 198 may be 



collected in almost any pond or stream where 

 vegetation is thick. The food of all of these 

 molluscs consists of vegetable matter, and when 

 planted in a pond with growing plants they will 

 reproduce at an enormous rate. 



Aquarists have introduced an African snail of 

 the genus, Limna?a, which has been successfully 

 bred in large numbers in a pond at Ithaca, 



Fig. 191. — Nymph of 

 mayfly 



FlQ, 192. — Adult mayfly 



Fig. 193. — Damsel flies: i, 2, 3, adults; 4, 5, 

 nymphs 



