276 THE GERM-PLASM 



tions which we have presupposed will, however, hardly exist all 

 together, but they may concur approximately with regard to a 

 certain number of characters. 



It can hardly be doubted that the second kind of cojitbination 

 occurs, and that in some cases the offspring take after one or 

 other of the parents only, — not only in respect of those charac- 

 teristics with regard to which the term • resemblance ' is generally 

 applied, such as those which concern the form and expression 

 of the face, but equally as regards stature, form of the body, 

 proportions of the limbs, nature of the skin and hair, character, 

 and temperament. 



We are met with a two-fold difficulty in attempting to explain 

 these facts : in the first place, how is it possible for all the pri- 

 mary constituents of one parent' — e.g., the father — to be pres- 

 ent in one of the germ-cells of this parent, as the germ-plasm 

 was halved by means of the reducing division before these germ- 

 cells become ripe ? — and secondly, how can it happen that the 

 maternal germ-plasm exerts no influence on the formation of 

 the child? 



Let us first consider the former of these two difficulties : how 

 is it possible for all the characters of the father to be con- 

 tained in one paternal germ-cell in spite of the reducing divis- 

 ion? If the latter process resulted in a quantitative halving 

 of the germ-plasm, no further explanation would be necessary, 

 for the qualitv of half the mass might be exactly similar to that 

 of the whole. But a reduction of the units of the germ-plasm 

 to half their number occurs in this process ; the number of ids 

 is reduced by one half, and the structure of the oflTspring results 

 from the combination in the germ-plasm of the ids of both par- 

 ents, as was shown in the case of plant-hybrids : it is difficult, 

 therefore, to understand why half the number of ids can never- 

 theless give rise to all the characters T)f the parent. Strictly 

 speaking, it is immaterial whether we concern ourselves with all 

 the characters, or with only a single one : for many characters, in 

 fact, depend on the co-operation of all the ids of the ontogenetic 

 stages in question. 



There is only one way out of this difficulty, — we must accept 

 the assumption, which has l)een confirmed by fact, that the 

 controlling power of the ids of one of the parents r/iay become 

 nullified at every ontogenetic stage. Obsen-ations on plant- 

 hybrids are invaluable in this connection, for in them we know 



