THE PROBLEM OF ACTIVATION' 257 



the cortical zone that were previously inhibited (Loeb, 

 R. S. Lillie). It is natural then to associate the rising 

 rate of metaboHsm with catalytic action, as Loeb has 

 done. But it should be borne in mind that this is 

 hypothetical, for such a reaction has not been demon- 

 strated. It is then supposed that, when these reactions 

 have been released, the complex mechanism of the egg 

 is set in action; but if the initial reaction is quanti- 

 tatively incomplete, or otherwise imperfect, the mechan- 

 ism stops sooner or later, owing in some cases perhaps 

 to too slow a rate, in other cases certainly to lack of 

 co-ordination. Such conditions are in some cases sus- 

 ceptible of adjustment by secondary treatments, as we 

 have seen. 



III. DISCUSSION 



I. The cortical changes. — Eggs that are artificially 

 activated always exhibit a marked slowness in rate of 

 development, even with the best methods, as compared 

 with fertilized eggs. This suggests some factor in ferti- 

 lization that has not yet been successfully imitated iii 

 any artificial way. But apart from this the activation 

 theories resulting from parthenogenesis are not directly 

 apphcable to the action of the spermatozoon. The 

 manner of activation must, however, be the same for 

 the most part; comparison of fertilization and parthe- 

 nogenesis should therefore serve to complete the theory 

 of activation. The most sigm'ficant factor that fertili- 

 zation has to add to the theory of acti\'ation would 

 appear to be the association of capacity for fertilization 

 (activation) with a diffusible substance or substances 

 (fertilizin) contained in the cortex of the egg. The 

 theory of artificial activation requires the presence of 



