XII.J CONJUGATION AND SEXUAL REPRODUCTION. 127 



cell the number of nuclear rods, and therefore the mass of 

 hereditary substance, is reduced to one-half. O. Hertwig 

 appears to accept my views as set forth above : at any rate he 

 thinks that I am ' on the right road in regarding the process by 

 which the second polar body is formed as a reducing process, 

 by means of which an amount of germ-plasm is removed, equal 

 to that which is afterwards conferred by the nucleus of the 

 spermatozoon.' Furthermore, his own account of the significance 

 of the process seems to agree with mine when he says — ' In 

 this very simple way it is brought about that the fusion of the 

 two nuclei resulting from the sexual act, — a union of the chro- 

 matin substance and the chromatin elements, — does not form 

 double the mass which is normal for the species concerned.' 



When, however, we remember that O. Hertwig rejects the 

 theory of ancestral plasms, and takes the antagonistic view of a 

 complete mingling of maternal and paternal germ-plasm,we must 

 be convinced that the reducing process, in the sense in which 

 I have spoken of it, has no existence for Hertwig, and that, 

 from his standpoint, the only conceivable theory is that of 

 a simple reduction of mass. And yet obviously such is not his 

 view, for he speaks of chromatin elements ; and hence the 

 question arises as to the kind of elements which these can be if 

 they are not ancestral plasms. It seems to me that the reducing 

 process only acquires a meaning when taken in connection with 

 the supposition of ancestral plasms, unless indeed it is merely 

 a matter of reduction of mass. But it is most improbable 

 that a mere reduction in mass is the object of this very remark- 

 able double division of the nuclear substance, which is never 

 again repeated in the whole developmental history of the 

 animal. First, the mass of nuclear substance is doubled, and 

 then reduced by two divisions to one-half its original bulk. 

 Obviously it would have been simpler if this process had been 

 omitted, and if the nuclear substance of the ^gg and sperm- 

 mother-cell had, during its growth, merely stopped short at 

 the requisite size. It may perhaps be objected that the growth 

 of the ovum and sperm-mother-cell and their histological 

 structure necessitate such a mass of nuclear substance. We 

 know little or nothing about the relationship of the mass of 

 nuclear matter to the mass of the cell-body, but it must 

 be doubted whether in this case the relation is fixed, because 



