238 MICROSCOPY FOR BEGINNERS. 



CHAPTER X. 



ENTOMOSTKACA AND PHYLLOPODA. 



THE reader is familiar with the crayfish, lobster, and 

 crab as members of that great group of animals called 

 the Crustacea, because they are covered by a hard, shelly 

 coating ; but, with the exception of the crayfish, he may 

 associate them all with salt water, while in reality our 

 fresh-water ponds are densely peopled with minute crus- 

 tacean creatures. The little fresh -water animals are 

 often enclosed in a bivalve shell, which some of them 

 have the power to open and shut ; or the back of the 

 body may be simply hardened, but without a distinct 

 shell. The feet, or legs, are usually numerous, and 

 very hairy or bristly, and in one section of those re- 

 ferred to in this chapter are flattened, and each one 

 bears near the body a flattened plate; consequently, 

 since these parts are somewhat leaf-like, the animals 

 have, as a class, been called the leaf-footed or the Phyl- 

 lopoda, which is putting the words into Greek. Yery 

 many others, to be found much more abundantly and 

 frequently than the Phyllopoda, are without these plates, 

 although the feet are as numerous and, in some, almost 

 as flat, and the shells or the shelly back as well marked. 

 These have been, by naturalists, grouped together under 

 the name of the Entomostraca, meaning little animals 



