ACTIVATION OF UNFERTILIZED STARFISH EGGS. 



279 



portion of eggs — 10 per cent, or more; In the second column the 

 least exposure at which any eggs (> I per cent.) formed larvce; 

 in the third the optimal time of exposure; and in the fourth the 

 longest observed exposure at which any eggs (> I per cent.) 

 formed larvae. 



If the several observed durations at each temperature are 

 averaged, the following results are obtained (Table X.) ; the 

 values are given in approximate terms rather than strict arith- 

 metical averages, to emphasize the fact that the precise durations 

 vary to a certain degree, even in normal eggs. There is, however, 

 for each temperature a well-defined modal duration of exposure 

 for producing a definite physiological effect such as membrane- 

 formation or complete activation. 



Table X. 



Approximate Times of Exposure Required to Produce the Following 

 Effects at Different Temperatures. 



It will be noted (i) that for each temperature there is a 

 minimum effective exposure which induces membrane-formation 

 followed by failure to develop and early breakdown; and (2) 

 that an exposure of approximately twice the minimum for 

 membrane-formation is required to enable even a few eggs to 

 develop to larval stages, and an exposure of three or four times 

 this minimum to enable development to proceed normally in 

 all eggs; and (3) that if the exposure is prolonged to about one 

 and a half times this optimum the eggs are again incapacitated 

 from further development. The fact that the ratios of the dura- 

 tions required to produce these several effects are approximately 

 the same at any one temperature indicates that a single process 



