884 The Outline of Science 



tingent carrying the factor for tallness and the other contingent 

 carrying the factor for dwarf ness. In other words, each germ-cell 

 is "pure" with respect to the factor of any particular unit- 

 character. Suppose a long-haired rabbit crossed by a short- 

 haired rabbit, the offspring will be all short-haired. But out of 

 eight ova produced by a female hybrid offspring, four will have 

 the factor for long hair and four the factor for short hair. Simi- 

 larly, out of eight sperm-cells produced by a male hybrid off- 

 spring, four will have the factor for long hair and four the factor 

 for short hair. Suppose these hybrids interbreed, and the fertili- 

 sation of the ova by the spermatozoa is fortuitous, then two egg- 

 cells with the short-hair factor will be fertilised by two sperm-cells 

 with the short-hair factor, yielding two quite pure short-haired 

 offspring; two egg-cells with the long-hair factor will be 

 fertilised by two sperm-cells with the long-hair factor, yielding 

 two quite pure long-haired offspring; two egg-cells with the 

 short-hair factor will be fertilised by two sperm-cells with the 

 long-hair factor, yielding two impure short-haired offspring like 

 the hybrid parents; and, finally, two egg-cells with the long-hair 

 factor will be fertilised by two sperm-cells with the short-hair 

 factor, yielding other two impure short-haired offspring like the 

 hybrid parents. So the result must be two pure short-haired 

 offspring, plus four impure short-haired offspring, plus two pure 

 long-haired offspring. If the impure short-haired rabbits are 

 interbred, their offspring (the third filial generation) will show 

 the same ratio, 1 : 2 : 1, more and more exactly the larger the 

 numbers dealt with. 



8 



Germinal Continuity 



One of the great post-Darwinian advances is the recognition 

 of the fact of germinal continuity made clear by Galton and 

 Weismann. While most of the material of the fertilised ovum 

 is used to build up the body of the offspring, undergoing in a 



