470 HEREDITY AND DEVELOPMENT 



ascending line through selection yielded to the old-established 

 combinations ? After a period of nutrition, however, they were 

 strong enough to assert themselves. Give them time, Prof. Ewart 

 says, and they will become so prepotent that they may hand on all 

 the peculiarities ever when the pigeon is crossed with another breed. 



Similarly, the first fertilised almost immature ova of a rabbit, 

 liberated by an ovulation subsequent to the first serving, result in 

 offspring which take after the male. In the fertilisational struggle 

 the paternal determinants have the mastery. If, on the other 

 hand, a doe is served, not at the right time, but a week or ten 

 days after, when the next young come they are all exactly like 

 the mother. The expression of inheritance is after the parent 

 whose germ-cells were the riper. 



These results, Prof. Ewart said, " were altogether different from 

 Weismann " ; from another point of view they are altogether 

 illustrative of Weismann's theory of germinal selection. 



Conclusion. If we accept the concept of ancestral plasms 

 that is to say, the idea that an inheritance is a mosaic of ancestral 

 contributions, and that a complete hereditary equipment is 

 present not merely in dual but in multiple form within the 

 fertilised egg then we pass naturally enough to the idea of 

 a struggle among the hereditary tendencies, which Darwin 

 indeed suggested which Weismann, however, has elaborated 

 into a fascinating hypothesis. 



If there are multiple analogous but not identical deter- 

 minants corresponding to any independently variable and 

 heritable part of the organism, what is to decide the expression 

 of these ? It is plain that the organism is not usually a melange 

 or blend of the ancestral contributions which made up its 

 inheritance. Must we, then, simply fall back on the general 

 assumption of a regulative entelechy which determines the deter- 

 minants ? In other words, perhaps, is the mysterious unity of 

 the organism, which applies to the fertilised egg-cell as well as 

 to the full-grown creature, such that it determines, by the very 

 fact that there is a unified organisation, which determinants 



