350 THE GERM-PLASM 



inasmuch as it results in the halving of the germ-plasm itself. 

 It became apparent subsequently that both divisions serve this 

 purpose, and each of them causes the removal of germ-plasm, 

 and not of oogenetic idioplasm from the ovum. 



My hypothesis must therefore be given up, but I nevertheless 

 believe that the conclusion on which it was based was a correct 

 one, and that it may be further utilised in the light of the theory 

 of heredity here developed. The oogenetic idioplasm must 

 exist, and, using the terminology I have now adopted, it may 

 be spoken of as the oogenetic ' determinant.' This determinant 

 will consequently be the first to become separated from the 

 mass of germ-plasm of the young egg-cell, to disintegrate into 

 its constituent biophors, and to migrate through the nuclear 

 membrane into the cell-body. In this way alone can we account 

 for no trace of it remaining in the nucleus, and for embryonic 

 development not being subsequently impeded by its presence. 

 This determinafit is used up, and disappears as sitch ; and the 

 fact that it is not expelled from the egg strongly indicates, if it 

 does not prove, that the control of a cell by a determinant is 

 accompanied by the absorption of the latter, and a further sup- 

 port may thereby be obtained for the hypothesis of emigration. 



A precisely corresponding process must be assumed to occur 

 in the formation of the sperm-cells, in which also the function 

 of the idioplasm during the histological differentiation of the cell 

 differs widely from that of the germ-plasm of the mature sperma- 

 tozoon. The necessity for assuming the existence of 'histoge- 

 netic ' determinants is perhaps rendered still more evident in the 

 case of the egg-cell, as in some animals two kinds of eggs are 

 produced which are very different as regards size, the relative 

 quantity of food-yolk, colour, and nature of the shell. The 

 assumption of iTvo kinds of oogenetic determinants cannot be 

 avoided in this case, for we cannot suppose that the same germ- 

 plasm can have such different effects on the cell. In the section 

 on alternation of generations, it was shown to be necessary to 

 assume that such species contain two kinds of germ-plasm, 

 containing determinants which are in part similar and in part 

 dissimilar. Thus the germ-plasm from which the winter-eggs 

 of the Daphnido' are developed must contain an oogenetic 

 determinant which is quite different from that of the germ- 

 plasm in the summer-eggs, for these two kinds of ova are 

 entirely dissimilar. 



