STRUCTURE AND DEVELOPMENTAL RATE 155 



The two groups that had been completely stopped in develop- 

 ment suffered very high mortalities. In each a considerable 

 majority of the eggs failed to resume development at room tem- 

 perature, and during the early days of development very many 

 of the survivors appeared abnormal in structure. These, how- 

 ever, later showed some ability to recover, but finally at an ad- 

 vanced stage about 33 per cent of them were still deformed. 

 In contrast to this, the eggs that had developed slowly at 9°C. 

 suffered only a low mortality on return to ordinary temperature 

 and there was not nearly so high a percentage of abnormalities. 

 At a late stage only 14 per cent were deformed as against over 33 

 per cent in the two other groups. The slowed group also hatched 

 earlier and with a better record than the two stopped groups. 



Similar differences in records between such groups of eggs were 

 often even better shown, as is indicated in the results of experi- 

 ment 902. In this case three lots of eggs in the two- and four- 

 cell stages were placed at 5° and 7°C. for four days, after which 

 interval they had divided four or five times and were all in about 

 the sixty-four-cell stage. They were almost, though not actu- 

 ally stopped, accomplishing only one cleavage per day. On re- 

 turn to room temperature, one of the lots from 5°C. suffered a 

 mortality of 78 per cent, only 22 per cent of these eggs being able 

 to resume development, although every one was developing when 

 first placed in the cold temperature. The lot from 7°C. showed 

 a mortality of 54 per cent. 



Another group of eggs from the same parents and accompanied 

 by the same control were placed at 9°C. at the same time and for 

 the same interval as the above lots. These eggs developed 

 slowly at 9°C., so that after their four-day sojourn they presented 

 high segmentation caps, similar to the condition of the control 

 after eighteen or twenty hours of development at normal tem- 

 perature. On return to room temperature, these slowly develop- 

 ing eggs resumed a normal rate and practically all formed em- 

 bryos. Thus, in respect to the number of embryos that were 

 developed, their record compared favorably with the control and 

 contrasted acutely with the only 22 per cent which resumed 

 development after the 5°C. interruption. The number of de- 



