EFFECTS OF HEAT ON TOAD*S EGG. 22/ 



A third part of the eggs remained at the temperature of 33-35 

 for three and one-half hours. These eggs were all dead when 

 removed from the influence of the heat. 



Experiment /./. A number of eggs in the blastula stage were 

 exposed to a temperature of 36-37 C. on April 26. Some of 

 the eggs were removed from the chamber at the end of one-half 

 of an hour. The eggs did not appear to be injured in any way 

 by the experiment and all developed normally. 



A second portion of the eggs from the above lot remained at 

 this temperature of 36-37 C. for three quarters of an hour. All 

 of the eggs gastrulated normally, but about half of them died 

 before the blastopore closed. When sectioned these eggs showed 

 no abnormalities. The rest of the eggs became normal embryos, 

 although developing very slowly. The medullary folds had 

 closed in the eggs of the control set when they were only begin- 

 ning to unite in the eggs that had been subjected to the increased 

 temperature. 



The remaining eggs of this lot were removed to room tem- 

 perature at the end of one hour. Although the eggs did 

 not appear to be dead when they were examined, they did not 

 gastrulate and none of them were alive the day following the 

 experiment. 



Experiment 15. Twenty eggs in late segmentation stages 

 were subjected to a temperature of 40-42 C. for one quarter of 

 an hour. Development was at once stopped by the heat, and all 

 of the eggs were killed. 



Experiment 16. When the dorsal lip of the blastopore was 

 just appearing, a lot of about twenty eggs was put into water 

 at a temperature of 33-35 C. and left there for three hours. 

 All of the eggs continued to develop somewhat more slowly 

 than the eggs of the control set and all became normal em- 



O C3 



bryos. 



Experiment 77. --On April 24, a lot of eggs in early gastru- 

 lation stages was kept at a temperature of 35-37 C. for one 

 hour. In all of the eggs the lateral and ventral lips of the blasto- 

 pore formed in the normal manner, but development stopped at 

 this point and the eggs died. No abnormalities were detected 

 when sections were made of several of these eggs. 



