Wniter Eggs 267 



ing, which, because of its saddle-shaped outHne,is called 

 an ephippium. This egg is liberated unhatched by the 

 molting of the female, as shown in figure 167. It 

 remains in its ephippium over winter, protected from 

 freezing, from drouth and from mechanical injury, 



Fig. 166. Ceriodaphnia bearing an ephippium containing the 

 single winter egg. 



and buoyed up just enough to prevent deep sub- 

 mergence in the mud of the bottom. With the return 

 of warmer weather it may hatch and start a new 

 line of parthenogenetic female Ceriodaphnias. 



Thus, it is that many organisms are removed from our 

 waters during a considerable part of the winter season. 



