ACTIVATION OF UNFERTILIZED STARFISH EGGS. 273 



than previously untreated eggs (cf. below, p. 288). Exposure 

 for 3 to 4 minutes induces typical membrane-formation in all 

 eggs, followed, however, not by cleavage and further develop- 

 ment but by irregular changes of form, fragmentation, and 

 eventual breakdown. With somewhat longer exposures (4 to 5 

 minutes) membrane-formation is followed by symmetrical cleav- 

 age in a certain proportion of eggs; and the proportion of such 

 cleavages, and also their approximation to the normal in rate 

 and character, show a progressive increase with increasing length 

 of exposure up to the optimum of about 8 minutes. With still 

 longer exposures the response again becomes unfavorable, and 

 eventually the eggs entirely fail to develop and even to form 

 membranes. We have here an apparent reversal of the rule 

 enunciated by Loeb with reference to the action of membrane- 

 forming agents on the sea-urchin egg. "A relatively brief 

 exposure to a cytolytic agent leads only to membrane-forma- 

 tion, while a longer exposure causes cytolysis."^ In the star- 

 fish egg a relatively brief exposure to warm sea-water (one just 

 sufficient for membrane-formation) is followed by an early 

 cytolysis, while a longer exposure results not only in membrane- 

 formation but in an approximately normal development; still 

 longer exposures again cause cytolysis without development. 

 This rule appHes to the action of cytolytic substances like fatty 

 acid, as well as to high temperatures (cf. below, p. 282). 



To illustrate the effects of exposures of different duration on 

 cleavage the following record is given (Table V.) describing the 

 condition of the eggs about four hours after exposure to 32° for 

 the times given. 



It will be noted that with brief exposures (3 to 4 minutes) 

 membrane-formation is typical, but the eggs are unable to cleave 

 normally and undergo irregular change of form followed by 

 breakdown. As the time of exposure increases, an increasing 

 proportion of eggs cleave, until the optimum (6 to 7 minutes) 

 is reached at which cleavage approaches the normal in rate and 

 character, and the great majority develop to larval stages. 

 Over-exposure (10 minutes) is again followed by failure of 

 cleavage and development. Similar observations were made 



1 "Artificial Parthenogenesis and Fertilization," 1913, p. 8. 



