Pearl, Reactions of Lhimbis. 153 



fore hatchincr and swimming would have gone on there if the 

 proper stimulus had been given. 



In order to get further evidence on this hypothesis experi- 

 ments were tried on hatched embryos, with a view of determin- 

 ing whether the chemical composition of the water influenced 

 the swimming movements. Embr}'os were put in solutions of 

 the following compositions : 



A. Fresh sea-water i part 



n 



NaCl I " 



10 



B. Fresh sea-water i part 

 Rain water i " 



The results so far as the swimming movements were con 

 cerned were essentially the same with the two solutions. There 

 was practically no swimming in the concentrated sea-water, and 

 very little in the diluted solution. Individuals would occasion- 

 ally make spasmodic beginnings of swimming movements but 

 these usually continued only for a few beats. The swimming 

 movements were better in the diluted than in the concentrated 

 sea-water, but in both series the total amount of swimming 

 done was very greatly reduced in comparison with what goes 

 on under normal conditions. Control series in normal sea-water 

 demonstrated that these results could not be due to light or 

 temperature effects. Other movements than swimming (walk- 

 ing, respiration, etc.) were not affected in solution B, and in so- 

 lution A only after the experiments had continued for over 48 

 hours. The sensitiveness of the embryos to chemical stimula- 

 tion was not apparently affected in either solution. 



These experiments, so far as they go, give confirmation to 

 the view that the necessary stimulus for the swimming reflex is 

 afforded by normal sea-water. It was impossible, on account 

 of lack of time, to absolutely prove that this is the case, but I 

 think we are justified in concluding that there is a considerable 

 degree of probability that this is the explanation of the fact 

 that swimming movements do not occur while the embryo is 

 within the "vicarious chorion," but begin immediately after 

 hatching-. 



