400 Ralph S. Li Hie 



but in the best experiment, that of July 29, the largest proportion 

 of regular cleavages — and in general the most favorable condi- 

 tions — was found in eggs w^armed at stages corresponding to 

 Nos. 8, 9 and 10 of the above table. 



In the series tabulated above the following chief uniformities 

 are apparent: (i) Warming shortly after removal (within 5 to 10 

 minutes, before the germinal vesicle has undergone any apparent 

 change) has the effect of completely preventing maturation; the 

 germinal vesicle remains intact and the egg remains permanently 

 in this condition until disintegration sets in. Such eggs behave in 

 the same manner as do eggs that fail to mature from any other 

 cause — they remain clear and apparently unaltered at a time 

 when mature eggs have undergone complete coagulation and dis- 

 integration. (2) Warming at'any time after the germinal vesicle 

 membrane has begun to dissolve and before the separation of the 

 first polar body may lead to development and production of larvae; 

 the proportion of eggs that develop is at first small, but increases 

 rapidly; in general the conditions for development steadily improve 

 until a certain stage is reached — about 40 to 45 minutes after 

 removal at normal summer temperature; at this time the suscepti- 

 bility of the eggs is greatest and momentary warming is followed 

 by development and the production of active larvae in a large pro- 

 portion. Thereafter the susceptibihty rapidly declines; and at the 

 time of separation of the first polar body warming results chiefly in 

 abnormal development and larvae are rarely obtained. 



Warming in later periods is still less favorable. In the following 

 two series eggs were treated as above at 10 minute intervals until 

 after the formation of both polar bodies, and after this less fre- 

 quently until about five hours after removal. Both series proved 

 favorable and showed good agreement; larvae were most numerous 

 from eggs warmed 10 to 15 minutes before the separation of the 

 first polar body; at the time of separation few or none were 

 obtained, and thereafter conditions became progressively more 

 unfavorable with lapse of time. After both polar bodies had 

 separated the eggs not infrequently failed altogether to cleave 

 or even to produce membranes — a result which agrees with those 

 of the earlier experiments already cited. 



