Artificial Parthenogenesis in Starfish Eggs 377 



follow warming to 35° or 40°; and a fundamental change in the 

 properties of the system and possibly a removal of the conditions 

 impeding spontaneous development might reasonably be expected 

 to result from such treatment. 



The failure of investigators in this country to obtain partheno- 

 genesis by elevation of temperature appears the less accountable 

 since Delage's descriptions are at least sufficiently definite to have 

 suggested a -procedure quite difi^erent from the one which was 

 actually employed and proved inefi^ectual. Thus Delage writes^ 

 "La temperature pent, a elle seul, surtout appliquee brusquement 

 a un stade critique, dont il va etre question, determiner la partheno- 

 genese chez Asterias." This critical stage is described as the 

 time (approximately) at which the nuclear membrane of the ger- 

 minal vesicle disintegrates allowing the nuclear contents to enter 

 the cytoplasm ; this event determines the time at which "merogonic" 

 fertilization becomes possible, and also artificial parthenogenesis 

 by heat: "at this moment the eggs of Asterias can be made to 

 develop parthenogenetically by simple immersion in water warmed 

 to 30° to 33°."^ The lack of exactitude in this description con- 

 sists chiefly in the failure to assign any definite limit of time to the 

 action of the warm sea-water. As will be seen below, this is a 

 matter of importance, since too long and too brief exposures alike 

 fail to produce the desired eff^ect and lead simply to abnormal 

 changes resulting in the early disintegration of the egg. It is 

 clear, however, that the eggs in Delage's experiments were warmed 

 for only a short period; in fact, he recommends placing the eggs 

 in warm sea-water contained in small vessels (cuvettes) which 

 may be rapidly cooled in running water. ^" In Greeley's experi- 

 ments the eggs (i) were allowed to mature — a necessary condition 

 for the production of parthenogenesis by cold, action of acids, 

 agitation, or hypertonic solutions, but one which precludes the 

 possibility of development by simple warming (as will be seen 

 below); and (2) were exposed to the high temperatures for periods 

 of an hour or more; whereas exposure to 35° for 60 or 70 seconds 



* Delage: Comptes rendus, cxxxiii, p. 348, 1901. 

 ' Delage: Comptes rendus, loc. cit., p. 348. 

 J" Delage: Archives de zoologie experimentale et generale, loc. cit., p. 309. 



