668 STUDIES IN GENEKAL PHYSIOLOGY 



and study of the eggs during the first seven to nine hours 

 is necessary. During this time the parthenogenetic eggs 

 throw out their polar bodies, segment, and become trocho- 

 phores, while the control eggs or the eggs treated with 

 ineffective solutions remain quite spherical and unchanged. 



The egg of ChaBtopterus is very 

 dark and opaque, and it is for this 

 reason much more difficult to deter- 

 mine the number of cleavage cells in 

 it than in the egg of most Echino- 

 derms. The fertilized egg of Ch?e- 

 topterus develops very quickly. At 

 a favorable temperature the cilia de- 

 velop five hours after fertilization, 

 and the larrce begin to swim. The 

 ^^^ development of the unfertilized eggs 

 / "*\ differs in most cases from that of 

 ( I the fertilized eggs. It is a little 



^ ' slower, and the nature of the seg- 

 mentation and the distinctness of the 



single cleavage spheres vary considerably with the nature 

 of the ions that are added to the sea-water, or the agency 

 employed to bring about artificial parthenogenesis. If K 

 salts are used, one does not, as a rule, notice much more of 

 the beginning development, except that the eggs become 

 irregular in their outline and amoeboid. In the experiments 

 with Ca salts and acids, the cleavage spheres were much 

 more distinct and regular. Fig. 157 gives a good average 

 picture of the amoeboid character of the K eggs. In the 

 experiment in which these eggs were drawn the unfertilized 

 eggs of a Chsetopterus were put into a mixture of 98 c.c. 

 sea- water-)- 2 c.c. 2^?i KC1 at 9:43. They remained in this 

 solution forty minutes, and were then put back into normal 

 sea- water. Three hours later, at 1:40, the drawing (Fig. 



