134 CHARLES R. STOCKARD 



The next experiment is cited to show the behavior of eggs 

 arrested in still later periods of general indifference. 



Experiment 907. — Eggs with germ-rings one-quarter to one-third 

 over the yolk sphere and with embryonic shields well formed, a stage 

 acquired after 48 hours of development during the early cool June 

 season, were placed in the refrigerator in two groups, Eo at 6°C. and 

 Eg at 8°C. 



After 24 hours in the refrigerator they had advanced only shghtly 

 beyond the condition of the day before. The E3 group had advanced 

 somewhat more than the E2 lot particularly in {he formation of the 

 embryonic line, or axis, in the shield. 



When 5 days old, and after having been in the refrigerator for 3 days, 

 the Eo group at 6°C. have advanced the germ-ring to about two-thirds 

 over the yolk sphere. Thej^ were thus not as completely stopped by 

 this temperature of 6°C. as were eggs placed in the same temperature 

 during early cleavage stages, as will be seen be3'ond. These eggs 

 were now, after 3 dscys of extremely slow development, returned to 

 room temperature. 



The E3 lot at this time showed the germ-ring almost completely over 

 the yolk-sphere, and the embryonic body was well formed in the ma- 

 jority of the eggs. These specimens at a shghtly higher temperature 

 had developed somewhat further than those above. They were now 

 also returned to room temperature. 



After being at room temperature for 24 hours, the rate of develop- 

 ment had greatly increased in both lots. The E2 group now showed 

 long embryos with the optic outpushings well begun in many. The 

 E3 lot showed optic outgrowths well formed in all, and were thus a little 

 ahead of the E2 ones in development. 



At 9 days old, the specimens in both lots seemed behind the control 

 to the extent of their 3-day stay in the refrigerator. 



When 12 daj^s old, they were closely examined for slight anomalies. 

 The E2 lot showed one abnormally small embryo with no blood cir- 

 culation, 4 had stopped, and did not develop after removal from the 

 refrigerator, and 45 specimens seemed to be in normal condition. 



The E3 lot all appeared to be normal except that the}^ were about 

 3 days behind the control in their development. 



Thus subjecting the embryos to a severe reduction in developmental 

 rate after they were 48 hours old had only slight, if any, detrimental 

 effect on their ability to resume a normal developmental rate and to 

 form apparently normal young embryos. Very probably, however, 

 minor effects are produced which would be indicated in the later struc- 

 tural or physiological history of the specimens could they be studied 

 through a longer season of their existence. 



At 19 daj^s old, when a large majority of the control had hatched 

 and were free swimming, none of the Eo or E3 lots had hatched. But 

 when 21 da3's old, a number were hatched in both lots. 



