THE GERM-PLASM 55 



number of units, on the variation of which the independent 

 changes of certain parts of the body depend. 



In all the higher animals the number of these units must be 

 very large, because the parts which are independently variable 

 from the germ onwards is large also. 



A consideration of the individual and hereditary characters in 

 the human species will show most clearly how great this number 

 may be. I know of a family in which a depression of the size 

 of a pin's head in the skin in front of the left ear has been 

 transmitted through three generations. This slight abnormality 

 must therefore have been contained potentially in the germ- 

 plasm of the respective individuals, and their germ-plasm must 

 ditfer from that of other people in the slightly abnormal form of 

 the element which determines this peculiarity. We are logi- 

 cally compelled to assume a particular element of the germ- 

 plasm for each peculiarity of this sort, not because heredity may 

 be manifested in details so minute, but because the tra7istuission 

 of such details 7)iay be independent. If all people possessed such 

 a depression in front of one ear, we could not thereby conclude 

 that it must be represented by a special element in the germ- 

 plasm merely because it is hereditary. It might conceivably be 

 represented, together with the skin of half the face, by one 

 element or biophor, which in the course of ontogeny became 

 divided into a number of secondary ones of divers sorts, one of 

 which proved to be abnormal and came to be situated at that 

 particular spot in the skin. What compels us to accept the 

 above assumption is the fact that all people do not possess this 

 depression, and that two persons might conceivably resemble 

 one another in all other respects except in the possession of this 

 abnormality. The germ-plasm of both these persons would be 

 almost identical, but not perfectly so, for it would contain a 

 certain element which differed in the two cases. This simply 

 means that this particular character which is independently 

 variable from the germ ofiwards is also represented by a special 

 element in the gertn-plasm. It would not have been possible to 

 infer this from its transmissibility alone. A hundred different 

 characters might conceivably be determined by a single element 

 in the germ-plasm ; the whole hundred would then be trans- 

 mitted as soon as the determining element was present in the 

 latter, but not one of them would be independently variable 

 from the germ onwards ; but if the determining element varied. 



