EFFECTS OF AMPHIMIXIS ON ONTOGENY 271 



and I believe that they are principally due to the fact that the 

 number of Iioinodyuaiiioiis detenitiiiants in the idioplasm of a 

 cell may vary in the course of ontogeny, and t/iat, in fact, it must 

 always do so. In one stage or in one organ the paternal, and 

 in another the maternal ids will contain the majority of homo- 

 dynamous determinants, and the fluctuations in the predominance 

 of the maternal or paternal characters, which is definitely deter- 

 mined in advance, must depend on this fact. 



To make this clear. I must intrench somewhat upon the 

 chapter on Variation. 



b. Intercalary Remarks on Variatio7i 



Hitherto we have assumed that the germ-plasm of a species is 

 composed of ids. each of which contains all the characters of 

 the species. A brief consideration, however, shows that this 

 cannot be the case. Not only is it conceivable, but it is even 

 necessary to assume that the development of the characters of 

 the species, as well as those of the individual, is only the 

 expression of the forces to which these processes are due. the 

 ids in which the forces are situated being by no means perfectly 

 similar to one another. A great majority of the ids certainly 

 contain all the determinants of the species. — that is, thev are 

 capable of giving rise to all the specific characters : but in a 

 minoritv of the determinants, to which, indeed, the oriorin and 

 development of this species was due. will not yet have begun to 

 undergo a phyletic transformation. All the determinants in this 

 minority need not necessarily be similar to one another ; one 

 id, for instance, may contain unmodified determinants of the 

 ancestral species ; while another, although still retaining some of 

 the old determinants, may exhibit a greater resemblance to the 

 pure ids of the existing species, and so on. Such a gradual 

 transformation of the ids affecting the majority of their deter- 

 minants must constitute, indeed, the process of the formation of 

 the species : and it will be quite in accordance with the principle 

 of variation to assume that modifications must take place in 

 the invisible vital units of a lower order, viz., the ids and 

 biophors, in exactly the same way as they occur in different 

 degrees and directions in different individuals in the visible 

 vital units, — the unicellular organisms and persons of stocks. 



Thus the pro-,'isional hypothesis put forward above, that the 

 gertn-plasm of a species — as far as it concerns the specific char- 



