ON THE CONDITIONS OF ACTIVATION OF UNFER- 

 TILIZED STARFISH EGGS UNDER THE INFLUENCE 

 OF HIGH TEMPERATURES AND FATTY ACID 

 SOLUTIONS.! 



ralph s. lillie. 



Introductory. 



In a former paper^ I showed that brief exposure of the un- 

 fertilized eggs of Asterias forbesii to temperatures of 32° to 38° 

 resulted in membrane-formation, cleavage and development. 

 With normal eggs and the proper times of exposure almost every 

 egg developed to a free-swimming larval stage; this treatment 

 thus forms a highly effective parthenogenetic method. The 

 time of exposure to the warm sea-water required to produce these 

 effects is definite (within a certain slight range of variation) for 

 any given temperature and decreases rapidly as the temperature 

 rises. Thus, as regards the least exposure necessary for the 

 formation of typical fertilization-membranes: "At 33° exposure 

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

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

 30 seconds, at 37.5° between 5 and 15 seconds, and at 40° momen- 

 tary exposure (5 seconds) produces membranes in practically 

 all eggs."^ The exposure required to induce development to 

 larval stages was found to be considerably longer than for 

 simple membrane-formation; at 35° from 70 to 90 seconds was 

 required, at 36° from 50 to 60 seconds, at 37° from 30 to 35 

 seconds, and at 38° about 20 seconds. The responsiveness of the 

 eggs to this form of treatment was found to depend on the stage 

 of maturation; warming before the dissolution of the germinal 

 vesicle had begun was ineffective and in fact inhibited matura- 

 tion entirely; the most favorable period lay between the break- 



1 From the Marine Biological Laboratory, Woods Hole, and the Biological 

 Laboratory, Clark University. 



2 Journal of Experimental Zoology, 1908, Vol. 5, p. 375. 



3 Loc. cit., p. 384. 



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