Adaptation to Environment 323 



months. Hence the eyes which were no longer in 

 connection with the central nervous system, which 

 had received no light, and could not have functioned, 

 regenerated and remained normal. The degeneration 

 which took place in the eyes immediately after being 

 transplanted was apparently due to the interruption 

 of the circulation in the eye, and the regeneration 

 commenced in all probability with the re-establishment 

 of the circulation in the transplanted organ. 



In our own experiments it can be shown that the 

 circulation in the embryo was deficient in all cases 

 where the eyes degenerated. The hybrids between 

 Fundulus and Menidia have often a beating heart but 

 rarely a circulation (although they form blood); and 

 the same phenomenon occurred in the embryos which 

 were exposed to a low temperature at an early period 

 of their lives. Hence all the facts agree that conditions 

 which lead to an abnormal circulation (and conse- 

 quently also to an abnormal or inadequate nutrition 

 of the embryonic eye) may prevent development and 

 lead to the formation of blind fishes. Eigenmann 

 states that no blood-vessels enter the eye of the blind 

 cave salamander Typhlotriton. The presence or ab- 

 sence of light does not usually interfere with the circu- 

 lation or nutrition of the embryonic eye, and hence 

 does not as a rule lead to the formation of degenerated 

 eyes. 



This would lead us to the assumption that the blind 



