PARTICULATE INHERITANCE 115 



or the one iris shows different patches of colour " (Pearson, 1900, 

 p. 452). The case of an English sheep-dog with a paternal eye 

 on the one side of its head and a maternal eye on the other is 

 vivid enough. 



When there is a marked difference in the pedigree, the vigour, 

 the age in short, in the constitution of the two parents, the 

 same mode of inheritance may be illustrated in a succession of 

 offspring. Thus a fine sire, paired with a commonplace mate, 

 may be prepotent birth after birth ; or a young mother mated 

 with a worn-out male may have it all her own way in regard to 

 inheritance, as well as in much else. On the other hand, when 

 there are no such marked differences between the parents, the 

 inheritance may be a blend in one offspring, exclusive in another, 

 particulate in a third. Moreover, in the same offspring, different 

 sets of characters may illustrate different modes of inheritance. 

 Thus we see that these modes of inheritance are merely useful 

 descriptive terms, helping us to keep our facts in order, but not 

 directly aiding us in their interpretation. They point to the 

 need of some unifying conception, which shall enable us to 

 understand how all these alternatives are possible. 



In large families there is sometimes observable an interesting 

 change in the direction of preponderance in the successive 

 children. With a virile middle-aged father and a much younger 

 mother, the older children may be markedly paternal in the 

 expression of their inheritance, the younger children as markedly 

 of the maternal type. The Benjamin is the mother's very 

 image, and after the father's own heart. 



Similarly, it has been observed that the first fertilised, almost 

 immature ova of a rabbit, liberated by an ovulation subsequent 

 to the first pairing, resulted in offspring which took after the male. 

 If, on the other hand, the doe was served, not at the right time, 

 but a week or ten days later, the young were all exactly like the 

 mother. 



Such cases suggest the conclusion that the expression of 



