STEUCTURE AND DEVELOPMENTAL RATE 145 



normal with a good circulation; very few were slightly deformed with 

 poor or no circulation. 



The majority in all B lots were now normal in appearance with a 

 good circulation. In the B3 lot 47 seemed normal out of 61, so that 

 14, or about 25 per cent, were abnormal, and of these 6 showed the 

 early cell-mass condition or were not developing. Thus only 8 

 embryos were smaller or slower than normal. Yet it must be recalled 

 that many dead eggs had been removed during the first few days 

 following return to room temperature. In the control, however, there 

 were no abnormal ones and there had been no unusual mortaUty. 



When 12 days old, the control were all normal and about in the 

 condition to hatch. 



In lot Bi 6 showed that development had stopped during an early 

 stage, 4 showed yolk-sacs with blood and pigment but no embryos, 10 

 were deformed embryos with no circulation, 4 were also deformed, 2 

 being eyeless, but with a circulation. Of all the survivors in this lot 

 24 were affected and 45 were apparently normal at this time, thus over 

 34 per cent were bad. 



In lot B2 14 failed to develop beyond the cell-mass stage, 4 pre- 

 sented only yolk-sacs with blood-spots and pigment cells, 8 were 

 abnormal with no circulation, and 3 were abnormal with a circula- 

 tion, while 31 appeared to be normal. Thus 15 of those that continued 

 to develop, or about 33 per cent, were abnormal and 25 per cent of the 

 total number that lived were unable to resume development after their 

 stay at 7°C. 



In lot B3 6 stopped development early, though continuing to live, 

 3 were deformed and possessed a circulation, 5 were deformed without 

 a circulation, and 47 individuals were apparently normal. Here, then, 

 only 14 per cent were deformed of those that developed. Such a 

 record is twice as good as that attained by either of the other groups. 

 Thus the 9°C. temperature, at which an extremely slow rate of de- 

 velopment is possible, is not so injurious to the later development of 

 those individuals which survive it as are the more severe temperatures 

 of 5° and 7°C., which practically stopped the progress of development 

 entirely. 



The control when 15. days old had not yet begun to hatch, on account 

 of the cool season. In lots Bi, B2, and B3 one or two more of the 

 abnormal embryos in each had died and all of the individuals were 

 behind the control in their developmental condition, though, as stated 

 above, many in all groups now appeared normal. 



When 19 days old, a large majority of the control were hatched 

 and swimming about in a typically active fashion. In lot Bi none 

 had hatched and several more had died. In B-^ none had hatched and 

 a few more also had died. In B3 none had hatched, many still seemed 

 nonnal, and many were deformed, showing distinctly typical eye 

 anomalies, cyclopia, etc., and there were many types of head and 

 caudal end deformities. 



THE AMERICAN JOURNAL OF ANATOMY, VOL. 28, NO. 2 



