150 CHARLES R. STOCKARD 



to the B control. These eggs, however, may be individually more 

 resistant. This lot was also now returned to room temperature. 



Lot B2, after 4 days at 7°C., showed some eggs with regular cleav- 

 age caps of 64 cells and more, but the majority showed caps of irregular 

 cell masses. These were now placed at room temperature. 



Lot Eg, after 4 days at 9°C., had all reached a high segmentation 

 stage comparable to about the condition of the control at 18 or 20 

 hours old. All of these eggs had a distended l)ubble-like segmenta- 

 tion cavity similar to that described by me ('06) as resulting from 

 treatments with LiCl solutions. Every egg was developing and fur- 

 nished a particular!}^ fine lot for an experimental test of this sort. 

 These also were now placed at room temperature. 



At 5 days old, the B and C controls were perfect with all embryos 

 developing well. In lot Bi the great majority had failed to resume 

 development after being 24 hours at room temperature. The seg- 

 mentation caps were breaking down and becoming disorganized. The 

 few specimens that had resumed development showed the germ-ring 

 formed and about one-half over the yolk-sphere. 



The lot B2 were in very nearly the same condition as Bi. 



In B3 the great majority were developing and the germ -rings were 

 here also about half over the yolk-sphere. 



Lot Ci showed many stopped in development, but here the major- 

 ity seemed well and showed the germ-ring about one-quarter over 

 the yolk. 



When 6 days old, the treated groups had been at room temperature 

 for 2 daj's, the Bi lot presented the following condition: Eight embryos 

 had formed, there was one yolk-sac with scattered cells, and 33 eggs 

 had died or failed entirely to resume development. All eggs in this 

 lot had originally begun development and the control from the same 

 group of eggs was perfect, thus the low temperature for 4 days had 

 caused a very high mortality. Only about 22 per cent of the eggs 

 resumed development. 



In lot B2 49 had formed embryos, 6 of these were short, lacking a 

 complete formation of their caudal ends, the others were well-formed 

 specimens with optic vesicles present. Fifty-eight did not resume 

 development, although all had begun before being placed in the cold, 

 thus there was a mortality' of 54 per cent in this group. 



In lot B3 practically all formed embryos which now showed optic 

 vesicles and body somites clearly formed. This lot was about as good 

 as the control in respect to the number of eggs developing. Thus a 

 4 days' sojourn at 9°C., with an extremely reduced developmental rate 

 did not prevent the possibility of again resuming a development of 

 normal rapidity. This extreme slowing at a slightly higher tempera- 

 ture is not nearly so fatal or injurious to later development as the almost 

 complete stop caused by the lower temperatures of 5° and 7°C. 



Lot Ci similarl}^ treated at 5°C., but consisting of eggs from another 

 parental pair, contained at this time 21 embryos with optic vesicles 

 forming, 7 short embryos with the germ-rings not completely over the 



