384 



Ralph S. Lillie 



TABLE I— Continued 

 Series III. August 6, igob. Eggs warmed during maturation process 



In general the above observations may be regarded as typical, 

 though I have found some variabihty in the readiness with which 

 eggs from different animals form membranes. But with star- 

 fish eggs in the early maturation period membrane-formation rarely 

 or never fails if eggs are exposed to temperatures between 33° and 

 40° for the periods indicated as optimal in the above table. The 

 result is remarkably constant, even if the subsequent cleavage and 

 development should prove abnormal or should altogether fail. 

 The facility with which the membrane is produced varies also in 

 eggs from the same animal at different intervals after removal; 

 in general the early maturation stages, before the first polar body 

 is separated, are most favorable; after the completion of matura- 

 tion, membrane-production is less regular and constant, and more 

 prolonged exposures to the high temperature are necessary. This 

 change is possibly to be correlated with the change in suscepti- 

 bihty to parthenogenetic development under this form of treatment, 

 which also diminishes after maturation is completed, as I shall 

 describe later. 



The minimum time of exposure necessary for membrane-pro- 

 duction is shown by the above experiments to decrease rapidly with 

 rise of temperature until a certain hmit is reached. At 33° expo- 

 sure must be prolonged to two minutes; at 34° the minimum lies 

 somewhere between 30 and 60 seconds; at 35° between 15 and 30 



