282 THE GERM-PLASM 



the other parent only. Homodynamous ids must, indeed, fre- 

 quently occur in both parents in cases of close interbreeding, as 

 well as in species which exist in comparatively small numbers 

 in small isolated districts. 



It is obvious that this struggle of the parental ids takes place 

 at every stage in ontogeny, and that its result is different 

 according to the state in which the forces exist at this stage. 

 This accounts for the frequent changes as regards the resem- 

 blance to one or other of the parents, and for the combination 

 of parental characters which occurs in different parts of the 

 body. 



The facts, so far as they are known to me, apparently agree 

 very satisfactorily with the above explanation. I have attempted 

 to collect fresh evidence bearing upon this question, which till 

 now has not been closely kept in view. This, however, has 

 unfortunately not been so easy a matter as might have been 

 expected, but I will mention some of the facts relating to this 

 point. 



In some cases a child resembles its father in most respects, 

 and takes after its mother as regards a few minor parts. This 

 would be inexplicable if the whole part were not controlled by 

 the resultant of a determinant other than that for the individual 

 portions of this part. The single determinant and its immediate 

 successors, which control the primary cell of the whole part, 

 determine, in the first place, the rate of the cell-division and the 

 primary form of the entire organ ; but in each subsequent stage, 

 one of the succeeding determinants takes on a controlling 

 function, and as its influence is always the resultant of the 

 homologous determinants of all the ids of the cell, the successors 

 of this cell may at any time differ from one another with regard 

 to their resemblance to those of the father or mother. 



A person of my acquaintance resembles his father very closely 

 in respect of that portion of the skin which is derived from the 

 external germinal layer. In both the father and son the epi- 

 dermis is thick and inclined to be horny. The nails of the 

 hands are much thickened, and the skin on the soles of the feet 

 is especially hard. In this case, therefore, the force-resultant of 

 the paternal determinants must continually have been stronger 

 than that of the maternal ones from the primary ectoderm 

 onwards, through a long series of cells. On the other hand, 

 the resultant of the maternal determinants seems to ha\e pre- 



