310 



THE EVOLUTION THEORY 



can only indicate that all parts of the cell have interrelations with 

 each other, and that, therefore, the division mechanism is dependent on 

 the condition of the rest of the cell-parts at the moment, and on the 

 substances which they contain or produce. From what we know 

 experimentally in regard to artificial parthenogenesis it is not difficult 

 to imagine that some sort of chemical substances are necessary to 

 stimulate the central corpuscle to activity. In any case, the whole 

 nutrition of the central corpuscle depends on the cell in which it lies, 

 as is shown by the fact that the sperm-nucleus, whose centrosome 



Ftg. 80. Fertilization of the ovum of a Gasteropod (Pkysa), after Kostanecki and 

 Wierzejski. A, the whole spermatozoon lies in the ovum, sp, its already divided 

 centrosphere. Rk i, the first polar body. Rsp 2, the second directive spindle. B, spk, 

 the sperm-nucleus, the second directive spindle still has its centrosphere, which 

 afterwards disappears. The first polar body (Rk 1) has divided into two. Highly 



magnified. 



before the entrance of the sperm into the ovum was inactive and 

 scarcely recognizable, grows rapidly after entrance and forms a large 

 aster round itself — is, in short, in the highest degree active (Fig. 80). 

 As the chromosomes certainly play an important part in the life of the 

 cell, and materially help to determine its various phases, it cannot be 

 disputed that they also may share in awakening the activity of the 

 central corpuscle. But this influence is only indirect ; it is not the 

 mere number of chromosomes that decides whether the central 

 corpuscle is to become active or remain inactive. This cannot be 

 assumed, because we have in the maturation divisions a proof that 



