254: MICROSCOPY FOR BEGINNERS. 



figure, so as to exhibit the single external ovary so 

 characteristic of it. 



12. CYCLOPS (Figs. 167, 167a). 



This commonest of all fresh-water Entomostraca has 

 a single eye in the middle of the forehead, like the 

 giants of ancient story, a bifid tail adapted for swim- 

 ming, and two external ovaries, 

 one on each side. These ovaries 

 are long, pear-shaped sacks filled 

 with dark, opaque eggs, and at- 

 tached to the body by the narrow 

 or stem end of the pear. The 

 young (Fig. 16 70) pass through 



Fig. 1<>7. Cyclops. , . . . 



several stages before they begin 



to resemble the parent. It lias been said that the eggs 

 are carried in the external ovaries only until they are 

 ready to hatch, when they are deposited before the 

 young make their escape. This is a mistake, as the 

 student will probably soon observe. The 

 young leave the eggs while they are still 

 attached to the parent. They break the 

 egg membrane very suddenly and unex- 



.j, i , , , . Young Cyclops. 



pectedly, although the observer may have 

 been for some time watching the little creatures rest- 

 lessly moving about inside. As they escape they often 

 dart half-way across the field of a low-power objective. 

 If Cyclops had no enemies the waters would soon 

 become filled with them in numbers almost beyond im- 



