THE BLINDNESS OF THE CAVE FAUNA. 67 



Amblyopsidae various mutations in the state of the eye may be 

 constantly arising (as in the case of Drosophlla) ; and some of 

 these mutants, especially those that are perfectly blind, can not 

 hold their own in the open while in the caves they can preserve 

 and perpetuate themselves. This assumption would not exclude 

 the possibility that Kammerer's observation may have been 

 correctly interpreted by him, it would only provide for the 

 possibility that his conclusion can not be generalized a possi- 

 bility which from the experiments mentioned in this paper 

 must be seriously considered. 



SUMMARY. 



1. It is shown that blind embryos or more correctly embryos 

 with degenerated eyes can be produced by heterogeneous hybridi- 

 zation in fish embryos (e. g., Fundulus heteroclitus 9 and Menidia 

 cf). Since in these cases as a rule no circulation exists the 

 inference is possible that the anomalous condition of the eye 

 may be due to lack of circulation. 



2. Blind embryos of the pure breed of Fnndulus heteroclitus 

 may be produced by the addition of KCN to the sea water. 



3. It is shown that immediately after fertilization (by sperm of 

 their own species) and during the early stages of segmentation 

 the egg of Fundnlns heteroclitus is rapidly killed or injured if it is. 

 exposed to a constant temperature of about o (or slightly 

 above) ; while it may be exposed to a slightly higher temperature 

 (e. g., 7 C.) for weeks without being injured. If the egg is 

 exposed to the low temperature after the embryo is once formed 

 it can resist the low temperature of from o to 2 C. for weeks 

 without permanent injurious effects. 



4. If eggs of Fundulus heteroclitus are fertilized with the sperm 

 of the same species and exposed immediately after fertilization 

 for a number of hours or a day to a temperature of between o 

 and 2 C. abnormal embryos can be produced a certain percentage 

 of which may show degenerated eyes. 



5. Lack of light does not influence the development of the 

 eyes of Fundulus. 



6. It is pointed out that internal mutational changes and not 

 lack of light may account for the blindness of certain cave fish 

 and salamanders. 



