274 AQUATIC MICROSCOPY FQR BEGINNERS. 



There are about thirty species of Cyclops, and in 

 each of them are four antennae, two being long and 

 conspicuous, the other two small, and often carried so 

 that they are invisible unless the Cyclops is turned on 

 its back. 



phyll6poda 



13. LiMN^Tis (Fig. 187). 



The oval or nearly spherical, smooth shell has a well- 

 marked beak, which in some of the species is enor- 

 mous, while in others it is less conspicuous. When the 

 valves are closed they measure about one-sixth of an 

 inch in length, and have often been mistaken for small 

 fresh-water mollusks of the genus Pisidium. The eyes 

 are two, but so close together that they often' appear 

 to.be united; they are black. The animals swim on 

 the back, as do so many of the Phyllopoda. 



In the males the two front legs are flattened, and 

 have on the end of each a complicated organ called the 

 hand, although it bears the most remote resemblance 

 to the human hand. 



The eggs are carried on the back under the shell. 

 The mature animals are flesh color. 



14. ESTH^RIA. 



The shell is smooth and shining, and marked with 

 distinct lines running alniost parallel with the front, 

 or free edge, of the valves. It is very thin, flat, and 

 large, measuring about two-thirds of an inch in length. 

 The males have two pairs of what are called hands, or 

 one on each of the four front legs. The shell of the 

 several species varies from oval to oblong with the up- 

 per margin~very much flattened, or it may be some- 



