IIKRKDITV AM) SEX 123 



])articulur colour, where .stock are heirii^ bnul, willi a view to 

 obtaini?i<^ tliat colour in tlie youn«<. 



Prepotknt'y 



It has lon^ been known to stock-breeders that certain sires 

 have the faculty of im[)ressinf^ their characters (or certain of them) 

 upon tlieir offspring, and when these qualities are desirable ones, 

 such a " prepotent " sire is of ^reat value as a stockcjc^ttcr. Thus 

 a ])u]l may be^jjet female })ro^eny which yield a higher ainounl 

 of milk than tfieir dams, and so be said to be prepotent for milk 

 production. Ft has been known also that inbreedinj^ favours 

 prepotency. In llie light of M(!ndclian inter|)retation pre- 

 potency is seen to Ik; a condition belonging to aninuils wln'ch are 

 homozygous for certain dominant factors or geiu's, anrl since 

 this condition in general is characteristic of ])ure bred and i!d)red 

 animals, it explains why these arc; so often prrpolcnl over cross- 

 f)red or mongrel ones. 



Thk Df<:tkrmina'I'T()N ok Skx 



We have seen already that the sexual union of the gametes 

 — ova and spermatozoa — is clearly foreshadowed among the 

 Protozoa in the process of conjugation. I>i-par(;ntal inheritance; 

 is universally correlated with all forms of conjugation, and it 

 may well be that we have here a chie as to the essential meaning 

 of the process. For conjugation, like fertilisation in the higlier 

 animals, is })roductive of variation, since the two gametes are 

 seldom or n(;ver absolutely identical. 



Variation in the Protozoa was presumal)ly originally due to 

 the direct action of the environment, which nnist differ slightly 

 even for two individuals living near together, while it is possible, 

 as we have seen, that even amorig higher forms, apart from the 

 endless variation caused by previous s(;xu;d union, the environ- 

 ment, acting through the bodily tissues, may exercise a general 

 influence on the germ cells, if not a specific one. 



It may be supposed that th(; production of further variation 

 induced by conjugation would have a survival value for the organ- 

 isms concerned, since there would be a greater chance of forms 

 suitable to the environment (which is always changing) being 

 l)rought into existence. The occurrence of gametic union wouM 



