ARTIFICIAL PARTHENOGENESIS AND FERTILISATION. 501 



admitted that, without prejudice to the question either of the 

 individuality, or the persistence of the centrosome, the body 

 and its aster represent a kinetic phase of protoplasm, which 

 reveals itself in cycles of activity, and that the ceuti-osomes 

 and asters constitute together, in some sense, a divisional 

 apparatus, though that term is not used in any definite 

 mechanical sense. 



The egg both before and after maturation lacks the power, 

 for and by itself, to produce in normal circumstances such a 

 divisional apparatus as will regularly and equally divide the 

 cell. 



In Ziegler's and Boveri's experiments on scpai-ated portions 

 of the egg containing only the egg nucleus, a divisional 

 apparatus is called up under the general stimulation of the 

 spermatozoon ; but it is ineffective, or only very partially 

 effective. In the etherised eggs it is slow in appearing*, and 

 less effective than that associated with the sperm nucleus. 

 In magnesium eggb the effect of the disturbance of equilibrium 

 is to cause a change of state in the protoplasm which results 

 in the differentiation at many foci of kinetic centres, and it is 

 only in the cases where a single such centre, which divides 

 into two, appears in the nuclear area, or at most tw^o centres, 

 that normal division proceeds. 



In fertilisation there is only one kiiietic centre, and this is 

 localised on the middle ^^iece of the spermatozoon. Its 

 activities are rapidly unfolded, and dominate all the other 

 latent astral activities of the egg. " The latent capacity of 

 both nucleus and cytoplasm to give rise to centrosomes is in 

 this case wholly inhibited."^ By union of the nuclei its 

 activity is transferred to the cleavage nucleus, and "becomes 

 a part of an activity on the part of the egg nucleus that 

 would have ensued even had the germ nuclei not united."^ 



Thus it may be said that the spermatozoon supplies the 

 lack in the egg, by providing a powerful and effective 

 "divisional apparatus. ^^ How is this effected? Does the 

 spermatozoon act by giving a general or diffused stinuilus 



' AVilson, 1001 a, pp. 5S1, 582. 



