THE PROBLEM OF ACTIVATION 263 



alone as the first readily observed evidence of activa- 

 tion, a slight increase in action of the agent may bring 

 eggs to the point of cleavage ; slightly more may induce 

 cleavage in a small proportion of the eggs; more yet a 

 larger proportion of normally developing eggs, up to 

 the optimum action, beyond which the reaction becomes 

 unfavorable (cf. R. S. Lillie, 1915). 



Under the second head it is not only necessary that 

 the rate and kind of metabolism should reach a certain 

 optimum, but also that the processes initiated should 

 be properly co-ordinated. Thus if the processes within 

 the egg exhibit a lack of co-ordination with reference 

 to regular segmentation, the entire developmental pro- 

 cess may go astray, whatever its rate. This is often 

 the case with artificial activation, as we have seen in 

 discussing the necessity for a double treatment in 

 parthenogenesis of the sea urchin (p. 243). 



In the case of fertilization, the karyokinetic phe- 

 nomena center around the sperm nucleus at first, and 

 the egg nucleus is later drawn into the same sphere of 

 influence. We have already discussed the theory that 

 the leading part taken by the sperm component is due 

 to a special organ (centrosome) intimately associated 

 with it (p. 71). There is no good reason for adhering 

 to this view, which has been quite generally aban- 

 doned. 



We have seen that spermatozoa that penetrate into 

 immature eggs, into eggs devoid of agglutinating sub- 

 stance, or into eggs already activated exert no effect 

 in the interior. As the spermatozoon produces no cor- 

 tical effect in these cases, we might generalize by saying 

 that a spermatozoon that has not been concerned in 



