Artificial Parthenogenesis in Starfish Eggs 409 



eggs, however, there is an obvious difference in the conditions; 

 the entire contents of the germinal vesicle — not only those sub- 

 stances that can pass the nuclear membrane — have become mingled 

 with the cytoplasm; and in fact mature eggs differ from immature 

 eggs in undergoing the typical disintegration much more rapidly 

 after forming membranes, as shown above. It is quite possible 

 that for the oxidations concerned in the post-maturative disinte- 

 gration of the cytoplasm there is needed the presence of specific 

 substances derived from the nucleus — e.g., oxidases, or enzymes or 

 proferments of some other kind, or certain activators — -and that 

 these substances merely find better conditions for their activity 

 after the separation of the fertilization-membrane than before. 

 In their absence membrane-formation would in itself effect no 

 esential change in the condition of the cytoplasm. Membrane- 

 formation alone is thus quite ineffective — unless accompanied by 

 certain other and independent changes — in accelerating oxidations 

 in the egg-cytoplasm. 



The effect of momentary warming in preventing the dissolu- 

 tion of the germinal vesicle is curious and difficult to explain. 

 The process itself, as shown by Loeb^^ some years ago, depends on 

 oxidations, since it is prevented by acidulation of the sea-water 

 or by depriving the eggs of free oxygen. One of his observations 

 seem analogous to the one under discussion; exposure of unripe egg 

 even temporarily (as for 15 jninutes), to acidulated sea-water 

 (100 cc. sea-water + 5 cc. yV HNO3) prevented the eggs from matur- 

 ing after retransfer to normal sea-water. An oxidative process 

 therefore which normally leads to the dissolution of the nuclear 

 membrane within a few minutes after the eggs are laid, if checked 

 before that time is ordinarily not resumed and the eggs remain 

 immature. But why should temporary warming at this stage 

 produce a similar result ^ The expectation would be that by 

 such treatment the oxidations, as well as the other chemical proc- 

 esses in the egg, would be accelerated, and that a process like 

 maturation, dependent on oxidations, would be furthered rather 

 than prevented. Evidently warming, during the brief period that 



31 Loeb: Archiv fiir die gesammte Physiologic, xciii, p. 59, 1902. 



