STRUCTURE AND DEVELOPMENTAL RATE 



127 



germ-ring had scarcely begun its descent over the yolk (fig. 3). These 

 also remained in the refrigerator. 



Lot Di after 45 hours at 5°C., was still in about the same stage of 

 development as when placed in the low temperature at 27 hours old. 

 These are now placed at room temperature. 



Lot D2 was in a closely similar condition to D,, but remained at the 

 reduced temperature. 



Lot D3 had also failed to make noticeable progress during the 45 

 hours at 8°C., but was allowed to remain at this temperature. 



Fig. 1 A control embryo 72 hours old, the body is well outlined and the 

 germ-ring almost completely over the yolk. 



Fig. 2 An egg 72 hours old that had spent the last 49 hours at a temperature 

 of 5°C. Development had been practically stopped in this high segmentation 

 stage. 



Fig. 3 A specimen 72 hours old that had been during the last 49 hours at a 

 temperature of 10°C. Development had progressed slowly, the germ-disc being 

 flattened and the embryonic shield, indicated by stippling, has just become 

 visible. 



