140 PRACTICAL ZOOLOGY 



water into their shell by movements of their feet and eating the 

 minute plants and animals contained in this water. 



Fresh- water Crustacea. --In fresh water, besides the cray- 

 fish, one is likely to encounter the fairy shrimp, the water flea, 

 and cyclops. The fairy shrimp, Branchipus (Fig. Si, C), is a 

 beautifully colored, almost transparent crustacean, one of the 



\ 



FIG. So. Several oysters to whose shells are attached many barnacles (near the 

 center) and mussels (below and at the sides). (From Bulletin U. S. Fish Com.) 



simplest of them all. It is often abundant in the spring in 

 ponds that later dry up. Here it swims slowly about on its back, 

 propelling itself by its leaf-like appendages. 



The water flea, Daphnia (Fig. 81, B), has a narrow body, re- 

 sembling a flea in this respect. It is protected by a heavy shell, 

 from the anterior end of which the large antennae are protruded 

 and moved, serving as swimming organs. 



Antennae are also used as swimming organs by Cyclops (Fig. 

 81, A). Individuals of this little one-eyed creature are present 

 by the million in almost every fresh-water pond. During the 

 summer the female carries a pair of brood pouches full of eggs* 



