THE GERM-PLASM 53 



the mother-cell, and thus the nuclear substance is always com- 

 posed of different kinds of biophors. But how does this apply 

 to multicellular forms in which so large a number of different 

 kinds of cells, each presupposing a different structure of the 

 nuclear matter, arises from the germ-plasm of the ovum ? Thus 

 we find ourselves brought back to the question asked at the end 

 of the last section : — on what do the regular series of changes in 

 the germ-plasm during ontogeny depend ? 



3. The Determinants 



As has just been shown, the nuclear matter of an Infusorian 

 must be composed of a great number of different kinds of 

 biophors, each of wiiich corresponds to the primary constituent 

 of a definite portion of the unicellular organism. If the cells of 

 a multicellular animal were represented in the germ-plasm by all 

 the kinds of biophors occurring in them, such an enormous 

 aggregation of biophors would result that, even if they were ex- 

 tremely small, the minute quantity of matter in the germ-plasm 

 would not be able to contain them. It was this consideration 

 more than any other which for many years made me persevere 

 in my attempt to discover an epigenetic theory of heredity. I 

 thought that it must be possible to imagine a germ-plasm which, 

 although highly complex, nevertheless did not consist of such an 

 inconceivably large number of separate particles, but which was 

 of such a structure as to become changed in a regular manner 

 during its growth in the course of ontogeny, and, finally, to yield 

 a large number of different kinds of idioplasm for the control of 

 the cells of the body in a specific manner. 



Hatschek,* too, has recently put forward the view that • the 

 egg-cell may be supposed to contain a relatively small number 

 of qualities,' and that this number is not larger than that which 

 is to be assumed in the case of any other histologically differen- 

 tiated cell of the body. The diversity in structure seen in 

 multicellular organisms is due, in his opinion, to the fact that 

 in spite of the limited diversity as regards the qualities contained 

 within a single cell (including the ovum), a far greater complica- 

 tion of the bodv as a whole is attained bv the variation of these 

 few qualities (' des einen Gmndthemas'). 



* B. Hatschek, ' Lehrbuch der Zoologie," 2te Lieferung. Jena, 1889. 

 p. 232. 



