412 - GRACE MEDES 



cumulatioD. The growth-curves indicate a considerable inhi- 

 bition during the first 24 hours, the period when the presence in 

 the medium of such substances as inhibit or accelerate growth 

 produces the greatest effect. The measurements for the suc- 

 ceeding days (aa) were 24 hours, 4.28; 48 hours, 56.18; 72 hours, 

 60.38; 96 hours, 60.47; and 120 hours, 58.47. 



In this solution a tendency toward radial arrangement of the 

 skeletal structures was evidenced in the early stages, followed by 

 irregularity in the later. Figures 143 and 144 represent speci- 

 mens at the 24 hour stage, and figure 145, at the end of 48 

 hours. Some, as in figure 146, have skeletons in one side only, 

 while others appear normal except for decreased size. The 

 animals had far from a healthy appearance, their movements 

 were less regular, and many had sunk to the bottom of the dish. 

 At the end of 120 hours a large number were dying. 



These modifications were not typical altogether of carbon 

 dioxide solutions, although the tendency toward radial sym- 

 metry is one of its characteristic effects. The abnormalities 

 caused by a medium which remains unchanged for several days, 

 is not then, due to the accumulating carbon dioxide alone, but 

 probably to the presence of other products of metabolism as 

 well. The dishes were shallow, and while they were closely cov- 

 ered to prevent evaporation, sufficient air-space was left above 

 the surface of the water to allow plenty of oxygen for the devel- 

 oping embryos. Vernon, by a gas determination, estimated that 

 the amount of oxygen in the water actually increased and the 

 amount of carbon dioxide in his cultures during the eight days 

 in which his experiments were run. Yet when such water was 

 used as a medium for a second culture, a decrease in size of 7.9 

 per cent and 7.3 per cent resulted. 



Another factor which might be exceedingly potent in deter- 

 mining the qualities and rate of development of the larvae 

 would be the degree to which the characters of the parents 

 are inheritable, and the extent to which these are modified in 

 different fertilizations. Since it was impossible to keep the 

 sea-urchins for two generations, an experiment was performed 

 similar to that done by Tennent ('10). He selected five fe- 



