STRUGGLE BETWEEN GAMETES 459 



involved in the fact that in some cases there are more ova than 

 sperms, though the reverse is usually the case. Thus Maupas 

 has shown that in Rhabditis and some other threadworms only 

 about a third of the ova can be fertilised ; there are no sperms 

 left for the other two-thirds produced later. 



Many other illustrations might be given, but our point here is 

 simply this, that a vivid realisation of the visible struggle among 

 germ-cells or gametes, and the frequently discriminate nature of 

 the ensuing elimination, may lead us naturally to an appreciation 

 of germinal selection which deals with the wholly invisible. 



Statement of Weismann's Theory. — As we have seen, Weis- 

 mann pictures the germ-plasm as composed of an army of living 

 determinants — that is to say, of an aggregate of primary consti- 

 tuents (or potentialities), of particular parts of the organism. 

 These particular parts will not arise if their determinants are 

 absent from the germ-plasm, and we know in some cases — e.g. in 

 the development of some Ctenophores (usually globular free- 

 swimming Ccelenterates)— that the abstraction of certain cells 

 from the embryo means an absence of certain structures from 

 the adult. 



Let us suppose, then, that the physical basis of inheritance is 

 composed of a multitude of representative vital particles, which 

 have the capacity of feeding, growing, and multiplying. As 

 the supply of nutriment necessarily fluctuates continually in the 

 reproductive organs as a whole, " we may therefore assume 

 that there are similar irregularities and differences in the 

 minute and unobservable conditions of the germ-plasm likewise, 

 and the result must be a slight shifting of the position of 

 equilibrium as regards size and strength in the determinant 

 system ; for the less well-nourished determinants will grow 

 more slowly, will fail to attain to the size and strength of their 

 neighbours, and will multiply more slowly " (1904, vol. ii. p. 117). 



Every one must admit that there are fluctuations in the 

 nutritive supply of the germ-cells, and to these, according to 



