EPIGENESIS OR EVOLUTION. 117 



the course of ontogeny the different kinds are sorted out 

 and arranged, so that the different cells come to contain 

 very different kinds of primordial particles, and therefore 

 that their capacity for further change is limited in every 

 stage by the particular kinds of particles which they 

 contain. 



This theory differs from that of the eighteenth century 

 in substituting for a preformation of organs as such, a pre- 

 determination of vital particles which by growth, multiplica- 

 tion and arrangement are to give rise to organs, or, at any 

 rate, are to control the formative processes by means of 

 which organs are established. But, as we have already 

 seen, the idea of preformed organs existing as such, but in 

 miniature, was by no means an essential part of the 

 physiological theory of the last century. Bonnet's final 

 conception of a germ as a " preformation originelle dont 

 un Tout organique peut resulter comme de son principe 

 immediat " is extremely like the modern conception of 

 germ plasm, composed of a multitude of predetermined 

 elements. 



A modern conception, derived from the theory of evolu- 

 tion in its larger sense, that is from phylogeny, is grafted 

 on the theory of individual evolution, and it is held to be 

 one of the great merits of the latter theory that it harmonises 

 and explains the analogies of ontogenetic and phylogenetic 

 development. This is the conception that the fixed archi 

 tecture of the germ is inherited ; that is to say, that it is 

 the necessary outcome of the architecture of the preceding 

 germ from which it was derived, just as that was the out- 

 come of the germ which preceded it, and so on in decreasing 

 circles of complexity to the beginning of living things. It 

 is impossible to follow out this idea with all its consequences 

 in the limits of an essay, but it is the essential proposition 

 which Weismann seeks to establish in his theory of the 

 germ plasm, and any one who wishes to understand the 

 subject better must be referred to his work. 



Bonnet and the older evolutionists were possessed of 

 a similar idea, which is in fact a direct corollary from the 

 theory of pre-existences or determinants. Since germs are 



