THE GERM-PLASM 6 I 



germ-plasm is capable of giving rise to the various kinds of 

 idioplasm required in the construction of the organism. 



As we have seen, the germ-plasm contains the primary con- 

 stituents of all the cells in the body in its determinants, and it 

 only remains to inquire how each kind of determinant reaches 

 the right part in the right number. Although we do not know 

 what forces are called into play for this purpose, the elements of 

 the germ-plasm now formulated, and the processes and course 

 of ontogeny, nevertheless enable us to draw certain conclusions 

 as to the structure of the germ-plasm and the nature of the 

 changes it undergoes ; and I trust that these conclusions will 

 not lead us too far from the truth. 



We can, in the first place, state with certainty that the 

 germ-plasm possesses a fixed arcJiitectiire^ wJiich has been trans- 

 mitted historically. In working out the idea of determinates, it 

 was stated that probably not nearly all the cells of the higher 

 organisms are represented in the germ-plasm by special deter- 

 minants : possibly all the blood-corpuscles, or the thousands of 

 fibres in a particular muscle, for instance, are represented each 

 by one determinant. But it does not therefore follow that all 

 the cells of a similar kind which exist in the body can be repre- 

 sented by one common determinant : this would be equivalent 

 to abandoning the conception of determinants altogether. If, 

 for instance, all the transversely striped muscles of a Vertebrate 

 were represented in the germ-plasm by a single determinant, 

 each variation in the latter would also produce a corresponding 

 change in all the muscles, and the independent variation of 

 which each individual muscle is actually capable would then be 

 impossible. 



Several, or even many, similar determinants must therefore 

 exist in the germ-plasm of an anijnal. Muscle-cells and nerve- 

 cells are repeatedly formed even in the fully developed organism, 

 and, in so far as they can vary individually at all from the germ 

 onwards, will be represented by identical or by very similar 

 determinants in the germ-plasm. 



If such identical determinants represent a single fixed cell or 

 group of cells, they cannot be situated anywhere in the germ- 

 plasm, nor can they change their position according to varying 

 influences : the determinants must be definitely localised, for 

 otherwise, they would not be certain to reach the right cell and 

 tiie right position in the course of ontogeny. 1 have already 



