THE BLINDNESS OF THE CAVE FAUNA. 63 



such a temperature for a month without suffering. The newly 

 fertilized eggs can, however, be exposed without injury to a 

 temperature of 7 for weeks and possibly longer. 



As already stated, among those eggs which were put into a 

 temperature of from o to 2 C. a certain number had defective 

 eyes. Thus the egg Fig. 10 w r as put immediately after fertiliza- 

 tion into a temperature of between o and 2 for twenty-four 

 hours and then put back to room temperature. The egg de- 

 veloped like a typical heterogeneous hybrid. Fig. 10 represents 

 the embryo when two weeks old; it had a beating heart but no 

 circulation. No eyes are noticeable. Fig. n represents an 

 embryo from another experiment; in this too the egg had been 



^-REMNANT Of EMBRYO 



BEATING HEftRT 



FIG. 12. 



kept for four hours (immediately after fertilization) on ice 

 (o to 2). Apparently no eyes are formed but the circulation is 

 established. 



Figs. 12 and 13 are added to show to what extent the abnormal 

 embryos, produced by a short exposure of the egg to a very 

 low temperature (o) immediately after fertilization, resemble 

 the monstrosities which are formed in the case of heterogeneous 



