142 CHARLES R. STOCK ARD 



weather of early June had caused this control to fall about 24 hours 

 behind in the four da3"s. Although such embryos appear to be nor- 

 mal, many of them are inferior in size and general appearance when 

 compared with more rapidly developing specimens of the later warmer 

 season. This advantage is no doubt due to the retarded development 

 primarily resulting from the cooler tempei'ature, and not to a poorer 

 quality of the eggs, since the midsummer eggs will fare in a similar 

 fashion when caused to develop at the same temperature. Such a 

 retardation, however, is too slight to produce gross defeats in any 

 average lot of eggs, yet the embryos very probably are somewhat below 

 par as their physiological responses would indicate. 



Lot Bi had now been for 2 days, 48 hours, at room temperature after 

 having spent 45 hours at 5°C. The germ-caps were about one-half 

 over the yolk-sphere, the germ-rings and embryonic shields were well 

 formed in most of them. The}^ presented the condition of a midsmn- 

 mer 24-hour stage, or were about up to the condition of the present 

 control at 48 or 50 hours. Thus during the 48 hours at room tempera- 

 ture these eggs had developed about as rapidh' as did the control during 

 their first 48 hours of development. 



The embryonic shields with the embryo in outline appeared normal, 

 although some were considerably behind others and a great many 

 failed to resmiie development after being removed from the refrigerator. 



The lot B2, after 24 hours at room temperature following a stay of 

 70 hours at 7°C., showed disc-like caps flattened down, but no germ- 

 rings were yet formed and the disc had not begun to descend over 

 the yolk-sphere. Some caps were still high or mound-like and many 

 were irregular, containing cells of different sizes (fig. 7). A large 

 number of eggs failed to resume development and there were many 

 discs with vacuoles in their centers, etc. 



The mortality resulting from this exposure was, therefore, high and 

 many embryos were rendered abnormal during these early stages. 



The lot B3, after 24 hours at room temperature, were in an even 

 worse condition than those in B2, although a single individual had a 

 germ -ring one-fourth over the 3'olk-sphere and was thus the most 

 advanced specimen of the two lots. The majority, however, presented 

 high germ-discs with a peculiar vacuole occupying about half of the 

 disc and distorting the position of the cells (fig. 8). 



Vacuoles similar in appearance are frequently present in eggs slowed 

 by other methods, such as solutions of LiCl, etc. But in this case the 

 vacuole differs somewhat in not being a simply distended segmentation 

 cavity. 



It will be recalled that these eggs developed very slowly at 9°C. for 

 70 hours, so that they had progressed much beyond the lots Bi and B2 

 when removed from the cold. Yet after 24 hours at room temperature 

 they were at a disadvantage rather than an advantage when compared 

 with Bo at this moment. The extremely slow progress during the 70 

 hours would seem to be more detrimental at this stage than the almost 

 complete cessation of development in lot B2. In later stages, however, 



