Artificial Parthenogenesis in Starfish Eggs 407 



yet. My own observations agree with Delage's and those of 

 later observers in indicating that the dissolution of the nuclear 

 membrane is in some way associated with a well-defined alter- 

 ation in the capacity of the egg for further development. Mo- 

 mentary warming previously to this event not only fails to result 

 later in cleavage, but it has the effect of completely preventing 

 the change in question and with it the entire maturation-proc- 

 ess. On the other hand, as already seen, the same treatment 

 applied at anytime after the beginning of the maturation-changes 

 (until the separation of the first polar body) may lead to develop- 

 ment and the production of larvae. The properties of the cyto- 

 plasm thus must undergo a profound change the nature of which 

 remains to be determined. 



One normal sequence of the dissolution of the germinal vesicle 

 is a change in the reaction of the egg-cytoplasm toward membrane 

 forming agencies. Membrane-formation now promptly follows 

 warming, or the entrance of a spermatozoon, or the momentary 

 action of a fatty acid or fat solvent; while in the immature egg this 

 structure is usually not formed under these conditions.-^ Yet, al- 

 though as a rule eggs that remain permanently immature as above 

 do not form fertilization membranes on warming, this is by no 

 means invariably the case. I have recorded numerous instances 

 in which momentary warming has produced perfectly normal 

 membranes in immature unfertilized eggs. In general such eggs 

 belonged to lots that were unfavorable as regards capacity for 

 development, so that the membrane-production may be considered 

 as evidence of a certain abnormality. The following instance will 

 illustrate: in the series of August 2, 1907, cited above, in which 

 eggs were warmed at 5-minute intervals (until the separation of 

 the first polar body in those maturing), the majority failed to 

 mature, and the developing mature eggs in no case reached the 

 free swimming stage. In this series most of the permanently im- 

 mature eggs, after subjection to the momentary warming process, 

 formed quite typical uniform membranes indistinguishable from 

 those found in fertilized mature eggs; this was especially true of 



23 Cf. Loeb: University of California Publications, Physiology, vol. ii, p. 150, 1905. 



