THE GERM-PLASM 63 



more especially those furnished by the phenomena of heredity 

 in sexual reproduction, lead us to assume that the germ-plasm 

 does not consist of a single id. but of several, or even many of 

 them, and this assumption must be made even in the case of 

 asexual reproduction. 



I shall therefore assume that each idioplasm is composed of 

 several or many ids, luhich are capable of growth and tJiultipii- 

 cation by divisio/i. If animals existed, in the whole series of 

 ancestors of which sexual reproduction had never occurred, 

 these ids would be exactly similar to one another. But in all 

 cases every id of the germ-plasm contains the whole of the ele- 

 ments which are necessary for the development of all subsequent 

 idic stages. Theoretically, therefore, one id would suffice for 

 ontogeny. 



We assume that the changes in the id of germ-piasfu during 

 ontogeny consist merely in a regular disintegration of the deter- 

 minants into smaller and smaller groups, until finally only one 

 kind of determinant is contained in the cell, viz., that which has 

 to determine it. It is highly improbable that all the determi- 

 nants in the id of germ-plasm are carried along through all the 

 idic stages of the ontogeny. In discussing regeneration and 

 gemmation later on, I shall have to show that, under certain cir- 

 cumstances, groups of determinants are supplied to certain series 

 of cells, and that these are not actually required for determining 

 the cells: this arrangement, however, depends, I believe, on 

 special adaptations, and is not primitive, at any rate not in the 

 higher animals and plants. Why should Nature, who always 

 manages with economy, indulge in the luxury of providing all 

 the cells of the body with the whole of the determinants of the 

 germ-plasm if a single kind of them is sufficient? Such an 

 arrangement will presumably only have occurred in cases in 

 which it serves definite purposes. The enormous number of 

 determinants contained in the germ -plasm also stands in the 

 way of such an assumption, for in the higher animals they can 

 be reckoned by hundreds of thousands at the very least ; and 

 although we may assume that they all remain in a latent condi- 

 tion in every cell, and so need not interfere with the activity 

 of the determinants which control the cell, they nevertheless 

 deprive the active determinants — which we must also suppose 

 to exist in large numbers — of a considerable space. 



If we wished to assume that the whole of the determinants of 



