268 THE INDUCTIONS OF BIOLOGY. 



This can have nothing to do with reducing the number of 

 chromosomes in the ovum. Unquestionably, however, this 

 change is included with the preceding changes in one trans- 

 action, effected by one influence. If, then, it is irrelevant to 

 the decrease of chromosomes, so must the preceding changes 

 be irrelevant: the hypothesis lapses. Contrariwise this fact 

 supports the view suggested above. That extrusion of a polar 

 body is a process of cell-fission is congruous with the fact that 

 another fission occurs after extrusion. And that this occurs 

 irregularly shows that the vital activities, seen in cell-growth 

 and cell-multiplication, now succeed in producing further 

 fission of the dwarfed cell and now fail : the energies causing 

 asexual multiplication are exhausted and there arises the 

 state which initiates sexual multiplication. 



Maturation of the ovum having been completed, entrance 

 of the spermatozoon, sometimes through the limiting mem- 

 brane and sometimes through a micropyle or opening in it, 

 takes place. This instantly initiates a series of complicated 

 changes: not many seconds passing before there begins the 

 formation of an aster around one end of the spermatozoon- 

 head. The growth of this aster, apparently by linear 

 rangings of the granules composing the reticulum of the 

 germ-cell, progresses rapidly; while the whole structure 

 hence arising moves inward. Soon there takes place the 

 fusion of this sperm-nucleus with the germ-nucleus to form 

 the cleavage-nucleus, which, after a pause, begins to divide 

 and subdivide in the same manner as cells at large: so 

 presently forming a cluster of cells out of which arise the 

 layers originating the embyro. The details of this process 

 do not concern us. It suffices to indicate thus briefly its 

 general nature. 



And now ending thus the account of genesis under its 

 histological aspect, we pass to the account of genesis under 

 its wider and more significant aspects. 



