268 



RALPH S. LILLIE. 



required temperature was reached; this temperature was then 

 kept constant during the period of the experiment by immersing 

 the beaker in a water-bath at the same temperature. At inter- 

 vals eggs were transferred to sea-water at room-temperature 

 contained in finger-bowls. The exposure to the warm sea-water 

 always took place during the interval between the complete 

 disappearance of the germinal vesicle and the formation of the 

 first polar body. 



Exposure to 28°, even if prolonged to 45 minutes, proved 

 almost entirely ineffective in forming membranes in starfish 

 eggs. With exposures of 30 minutes or more an occasional egg 

 may form a membrane, but the great majority always remain 

 unaltered. 



At 29° membranes appear in a considerable proportion of eggs 

 after exposures of 12 to 15 minutes. With longer exposures 

 (25 to 30 minutes) a majority in some cases (not always) may 

 form membranes, and a considerable number may develop to 

 larval stages. Table I. summarizes the results of two series of 

 experiments in which eggs were exposed to 29° for periods ranging 

 from 2 to 40 minutes. In both lots of eggs the great majority 

 underwent normal maturation, and a large proportion developed 

 normally to larvae after sperm-fertilization. 



Table I. 



29'- 



The two series show some minor differences, but in both the 

 number of eggs forming larvae is small, and a certain proportion 

 fail to form membranes even with the optimal exposures. This 

 temperature is near the lower limit below which the eggs show 

 no response to this form of treatment. 



