ACTIVATION OF UNFERTILIZED STARFISH EGGS. 



269 



At 30° the proportion of eggs forming membranes and develop- 

 to larval stages is higher than at 29°, although considerable 

 variability is still shown. Five series of experiments were 

 performed at this temperature. Table II. summarizes the 

 results of four of these.'^ Each lot of eggs was favorable, matura- 

 tion and development to larvae after sperm-fertilization taking 

 place in nearly all. Table II. gives the approximate proportion 

 of eggs forming membranes and developing to blastulae after 

 exposure for the periods given in the first column. 



Table II. 



30' 



It will be noted that in four out of the five series at 30° an 

 exposure of 8 to 10 minutes was required to cause membrane- 

 formation in 10 per cent, or more of the eggs; in the fifth series 

 (June 7) 5 minutes was sufficient. The proportion of eggs 

 developing to larvae was comparatively low in all series; the 

 optimum exposure lay between 24 and 28 minutes in the only 

 series (June 13) in which the proportion of larvae was consider- 

 able. With longer exposures membranes become fewer and there 

 is a rapid decline in the proportion of eggs forming larvae. 



1 In the remaining series the longest exposure was lo minutes, at which about 

 two thirds of the eggs formed membranes and a small number developed to larvae. 



