FACTORS IN ONTOGENY 251 



Niigeli, a philosophical botanist,, proposed a theory of germ- 

 plasm structure and behavior which may be called the theory 

 of micelhc, nutritive plasm and idioplasm. When the complex, 

 life-characterizing albuminous substances took their birth in an 

 aqueous liquid, they were precipitated as tiny particles called 

 micella 1 , which attracted other micella? to themselves and thus 

 produced aggregates of primitive life stuff, or protoplasm. The 

 micelke are all separated from each other by thin envelopes 

 of water, thus making water an integral part of protoplasm, 

 and making growth by intercalation of new micelhe possible; 

 this primitive protoplasm becomes arranged in two ways, 

 resulting in producing two kinds, one called nutritive proto- 

 plasm, and the other idioplasm or germ plasm, extending all 

 through the nutritive protoplasm as a fine network. 



Finally, the most recent micromeric theory of germ-plasm 

 structure is that of Weismann, the modern champion of natural 

 selection. According to him the protoplasm of the nucleus is 

 made up of units called biophors, which are the bearers of the 

 individual characters of the cell; the biophors are complex 

 groups of molecules, capable of assimilating food, growing, 

 and reproducing; the number of biophors is enormous, as it 

 must equal the possibilities of cell variety. The biophors are 

 united into fixed groups called determinants, each determinant 

 containing all the biophors necessary to determine the whole 

 character of any one cell; in each specialized cell there need 

 be but one determinant, but in the germ cells every kind of 

 determinant must be represented. 



In connection with the postulation concerning the ultimate 

 make-up of the plasm of the germ cell, Weismann has formu- 

 lated a theory of germinal selection to account for the obvious 

 fact that a certain cumulation of variation of a certain kind or 

 along fixed lines may take place without the aid of natural 

 selection: this variation cumulation often being indeed of a 

 degree too slight to give any opportunity for interference by 

 natural selection. To account for this fact, which has been 

 much used by adverse critics of natural selection, Weismann 

 assumes a competition of the determinants in the germ cells 

 for food, hence for opportunity to grow, to be vigorous, and to 

 multiply; the initially slightly stronger or more favorably 

 situated determinants will get the most food, lessening, at the 

 same time, the food supply of others. Now, when the germ cell 



