22O HELEN DEAN KING. 



The remaining eggs of this lot were kept at the temperature of 

 30-32 C. for one and one-half hours. At the end of this time 

 they were in the i6-cell stage, while the eggs of the control 

 set were only in the 2 4-cell stage. Later segmentation of 

 these eggs seemed to be normal, and on April 18 the dorsal 

 lip of the blastopore appeared in a very few of them. On the 

 morning of April 19 most of the eggs were dead, and not one of 

 them, when examined, was found to have gastrulated. In the 

 eggs still living the blastopore was closing in, but development 

 was much slower than that of the eggs of the control set in 

 which, at this time, the blastopore had already closed and the 

 medullary folds were forming. All of the eggs were dead on the 

 morning of April 20, and in no case was gastrulation entirely 

 completed. 



In these last two lots of eggs the injurious effects of heat 

 were not apparent during the segmentation stages and only 

 manifested themselves when the eggs were ready to gastrulate. 

 Early development was accelerated ; but later development 

 lagged behind, or, at most, was equal to that of the eggs in the 

 control set. 



Experiment j. A number of unsegmented eggs were exposed 

 to a temperature of 32 C. for two hours on April 22, and when 

 removed they were in the :6-cell stage. In this lot of eggs 

 the later cleavage was very abnormal as the upper hemisphere 

 divided into a number of small cells, while the lower part of 

 the egg segmented only a few times and, consequently, was com- 

 posed of a small number of very large cells. Cleavage lines 

 were very distinct in the upper part of the egg ; but it was almost 

 impossible to make out the boundaries of the yolk cells. None 

 of the eggs in this set gastrulated and all of them were dead by 

 April 24. 



Experiment /. On the morning of April 1 6, a small lot of 

 eggs was subjected to a temperature of 3233 C. for one-half 

 of an hour. The eggs had not segmented when they were put 

 into cooler water, but in every case the first furrow appeared 

 in about fifteen minutes. In the control set, the first cleavage 

 plane came in about half an hour later than it did in the eggs 

 used for the experiment. All of the eggs of this set developed 



