THE BLINDNESS OF THE CAVE FAUNA. 



59 



their development was retarded by putting them into sea water 

 to which some KCN was added. Fig. 9 shows a blind embryo 

 obtained in this way. The eggs were put immediately after 

 fertilization into a weaker solution of KCN in sea water where 

 they remained sixteen days. They developed slowly. The 

 embryo was drawn two days after it had been put back into 



FIG. 8. 



normal sea water. The heart-beat and circulation were estab- 

 lished. This method of producing blind embryos is not reliable 

 and need not be discussed any further. 



A better method was found by exposing the newly fertilized 

 eggs to a low temperature (from between o to 2 C.) for some 

 time. The writer found that the egg of Fundulus can be put 

 for weeks into such a low temperature after the embryo is once 

 formed, without any injury to the latter. As soon as it is put 

 back to room temperature it continues to develop. This corre- 

 sponds with the idea that the low temperature only retards the 

 chemical reactions underlying development. If, however, the 



