668 STUDIES IN GENERAL 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 Chetopterus 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 Che- 
topterus develops very quickly. At 
a favorable temperature the cilia de- 
velop five hours after fertilization, 
and the larve begin to swim. The 
development of the unfertilized eggs 
differs in most cases from that of 
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 amceboid character of the K eggs. In the 
experiment in which these eggs were drawn the unfertilized 
eggs of a Chetopterus were put into a mixture of 98 c.c. 
sea-water + 2 c.c. 24n KCl 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. 
FIG. 157 
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