STRUCTURE AND DEVELOPMENTAL RATE 169 



The two lots in the refrigerator at 22 hours old had as a rule under- 

 gone only one cleavage further than when placed in the cold. All 

 were in a rather typical 16-cell stage. The low temperatures had not 

 quite completely stopped development. 



At 48 hours old, the control embryos were in a very advanced con- 

 dition. They were large in size with fully formed optic cups and 

 lenses, about 10 to 12 pairs of somites, the pericardium distended and 

 the heart formed, although not yet pulsating. Chromatophores were 

 present and though small had already differentiated into the red and 

 black types. Five hours later the hearts were pulsating, but the blood- 

 vessels were not fully connected and there was no circulation. One 

 familiar with these embryos will realize that such a condition of develop- 

 ment is rarely attained in less than 70 hours, thus this control group 

 was developing with unusual rapidity. 



The eggs composing the Ai lot when 48 hours old at 6°C. were in 

 about 32- or 64-cell stages. Many of the blastoderms were discs of 

 irregular cell arrangement and some presented large uncleaved proto- 

 plasmic portions. The A2 lot were in a closely similar condition. 



The control specimens when 72 hours old had a vigorous blood 

 circulation, with the vessels already mapped out by the migrating 

 chromatophores. During the cooler, earlier part of the season a similar 

 condition was not reached in less than four days of development. 



The eggs in lot Ai, after being 69 hours at a temperature of 6l^°C., 

 all showed irregular segmentation caps, the cells of which seemed to 

 be in a large vesicle or bubble-hke formation. The caps appeared to 

 contain approximately 64 to 128 cells loosely arranged and in every case 

 located within the bubble-like area, which seemed to prevent the normal 

 flattening down of the cap upon the yolk-sphere. 



There seems to be a clearly marked surface film between the yolk 

 and the region containing the cleavage mass. It is as if the cleavage 

 mass existed in a drop of more transparent highly refractive fluid. 

 The drop is not in a segmentation cavity, but probably consists of 

 accumulated fluid such as normally exists in the cavity, but here located 

 between the cell mass and the yolk, possibly on account of some 

 peculiar osmotic effect. 



The specimens of group A2 kept at 8°C. were at 72 hours old in a 

 closely similar condition to those of Ai. Both groups were removed 

 from the refrigerator and placed at room temperature after this 69-hour 

 exposure to the low temperatures. 



After being out of the refrigerator for two days, many eggs in the 

 Ai and Ao lots had failed to resume development and had died. 



When 8 days old, or 5 days after removal from the low temperature, 

 many more, 41 of the remaining 99 eggs in lot Ai, were dead and many 

 of those living were grossly deformed. In lot A2 a few more were 

 dead, many were not developing, a number were grossly deformed, yet 

 some were apparently normal. 



When 10 days old, the eggs were all very carefully examined to 

 determine as nearly as possible the exact nature of the abnormalities 



