ACTIVATION OF UNFERTILIZED STARFISH EGGS. 287 



Experiments similar to the above were performed with pre- 

 liminary exposures to 32° of 2, 3 and 4 minutes, followed by 

 after-exposure to 32° as above for 4 minutes (in one series for 

 five minutes), all of which gave the same general result. Appar- 

 ently it is a matter of indifference whether the second exposure 

 to 32° follows immediately after the first or at an interval, 

 provided that the second exposure takes place before the separa- 

 tion of the first polar body. After this event there follows a 

 decided and rapid decline in the favorability of the response to 

 the after-warming treatment, and after the separation of the 

 second polar body after-warming is apparently quite ineffective. 

 As I described in my former paper on this subject, the suscepti- 

 bility to parthenogenesis by temporary continuous warming 

 always undergoes marked and rapid decrease at the time of the 

 maturation-divisions.! The above decline in the response to 

 after- warming is evidently the same phenomenon. A similar 

 decrease in the susceptibility of the eggs to sperm-fertilization 

 also takes place at about the same time, although this decrease 

 is not so pronounced as in the case of parthenogenesis ; thus it is 

 usually possible to fertilize a certain variable proportion of 

 starfish eggs (not all) after maturation has been complete for 

 some hours.2 The fact that the general responsiveness of the 

 egg to any activating agent undergoes a sudden decline at the 

 time of separation of the polar bodies suggests either that some 

 material necessary to development is then lost, or that a refrac- 

 tory state conditional on some other kind of change (possibly a 

 change in the plasma-membrane) then develops. As already 

 pointed out, the fact that sperm-fertilization is possible (although 

 less favorable) at a time when the egg fails to respond to the 

 parthenogenetic treatment suggests that some definite material 

 playing an important part in development is introduced into the 

 egg by the sperm. This is also indicated by the general fact 

 that sperm-fertilization induces a more favorable development 

 than artificial activation. It may be that this material is the 

 same as some substance lost from the egg at the time of the 

 maturation-divisions. Further research has to decide between 

 these possibilities. 



1 Loc. cit., 1908, p. 400. 



2 Loc. cit., p. 411. 



