128 CHARLES R. STOCKARD 



When four days old, the control embryos were fully formed with 

 prominent optic vesicles, hearts were formed, but not yet pulsating. 

 Thus they were not more than up to a midsummer 72-hour stage, since 

 the heart beat had generally begun about this time. However, all of 

 these embryos were normal and well, as is shown by their later records, 

 even though the cool season had thrown them about 24 hours behind 

 within four days. 



Lot Ci, now having been at room temperature for 24 hours, were all 

 going very well. The germ-rings varied in position from one-quarter 

 to one-third over the yolk-spheres. Only a few had failed to resume 

 development and the eggs in general were about up to the condition 

 of the present control when they were 50 hours old. These Ci eggs 

 had now actualh' developed at room temperature for about 47 hours, 

 the first 23 hours after fertilization and the fourth day. 



Lot C2 was also after similar periods of experience in a uniformly 

 good condition with the germ-rings all about one-third over the yolk- 

 spheres. Thus subjecting to low temperature after 23 hours of develop- 

 ment is decidedly less injurious than similar treatment during the 

 early cleavage stages, as will be seen from the records beyond. 



In lot C3 the germ-rings had all descended about half way over the 

 yolk-sphere. 



The D series showed somewhat the same response. Lot Di, after 24 

 hours at room temperature, were developing normallj^ with the germ- 

 rings from one-half to two-thirds over the j^olk-spheres and the em- 

 bryos well formed. Thus stopping for 48 hours after 27 hours of de- 

 velopment, when the segmentation caps were flattened over the top of 

 the yolk, showed no ill effects on their present development except to 

 render them almost exactty two days behind the developmental stage 

 of the control. 



The control at 5 days old had a vigorous heart beat, but the circula- 

 tion was just beginning to be well established. 



Lot Ci, almost all of the embryos were full length, the optic out- 

 pushings were just beginning, but not fully formed, thus about in the 

 condition shown by the present control at 72 hours. These were 

 still about two daj^s behind the control, or had practically lost the time 

 spent in the refrigerator. There were a few with the germ-rings not 

 entirely covering the yolk and with the body of the embryo short and 

 poorly formed at the caudal end. 



Lot Co were about in the same condition as Ci. 



Lot C3 seemed on the average a little further along, though closely 

 similar to the two foregoing lots. 



Lot C4, now four days in the refrigerator at 9°C., seemed in good 

 condition, with the germ-rings well formed and descended about one- 

 half over the yolk. These specimens had thus continued their de- 

 velopment at this temperature, although very slowly, and had ad- 

 vanced about 12 hours in development within the 4 days. They were 

 now returned to room temperature. 



