THE GEEM-PLASM THEOEY 347 



chromosomes the child will have in its cells two maternal chromo- 

 somes (A) and two paternal chromosomes (B) ; what form will this 

 proportion take in the germ-cells produced by the child? The 

 maturation division can effect the reduction to two chromosomes 

 in different ways; there may, for instance, be two paternal chromo- 

 somes (B) left in the one, and two maternal chromosomes (A) in the 

 other daughter-cell, or one paternal [B) and one maternal (A) in the one, 

 and a similar combination in the other cell. Let us follow the latter 

 case further. A sperm-cell which contained the combination A and B 

 might meet in amphimixis with an egg-cell of different origin also 

 containing a similar combination of chromosomes, let us say a chromo- 

 some C from the mother, and a chromosome D from the father. We 

 should then have in the segmentation nucleus of the fertilized ovum 

 four different chromosomes, each of which contained the hereditary 

 substance of one grandparent; we should have the four chromo- 

 somes, A, B, C, D, as the hereditary substance of the grandchild. 



But since, as ive have seen, the halved hereditary substance still 

 contains the whole mass of 2^'^i'^nary constituents, each one of these 

 chromosor)ies must contain the collective primary constituents of the 

 u'hole body of the relevant grandparent ^. The hereditary substance 

 in the fertilized ovum thiis consists of several comp)lexes of primary 

 constituents (chromosoTiies) each of tvhich (an 'id') comprises within 

 itself cdl the primary constituents of a complete individual. 



It can be made clear in yet another way that, as a consequence 

 of sexual reproduction, the germ-plasm of each species must be 

 composed of several ' ids,' individucdly different. Let us assume 

 that there was as yet no amphimixis, and that we could look on 

 at its introduction into the organic world; the hereditary substance 

 of the beings which had previously lived and multiplied hj division 

 would consist of more or less numerous chromosomes similar to each 

 other, so that, for instance, each individual would contain sixteen 

 identical ' ids.' But if amphimixis were now to take place for the 

 first time, in the same manner as it does to-day — that is, after 

 the reduction of the number of the ids to half — ^in the first amphi- 



' When I say the 'collective' primary constituents of the whole body of the 

 grandparent this is not expressing it quite precisely, for, as we shall see later, each 

 individual must arise from the co-operation of different chromosomes of different 

 origin, not merely fx'om one of the chromosomes contained in its germ-plasm. In the 

 example given above, the body of each grandparent cannot have arisen only from 

 a single chromosome, which was transmitted to his grandchild, but from the co-opera- 

 tion of this chromosome with three others, which have distributed themselves along 

 other genealogical paths. But this does not affect the above chain of reasoning, for 

 here it is not a question of whether all the primary constituents of the grandparent 

 are present in the child — that can never be the case — but whether the primary 

 constituents transmitted by him represent the whole body of an individual. 



