Ixsxii GENERAL INTRODUCTION. 



&c. In tlie same way, if only tlie units of the two germ- 

 cells whicli agree in structure and have a certain affinity 

 for eacli other are capable of forming stable combina- 

 tions, there must often be millions of units that fail to 

 enter into the composition of the new cell. 



According to Mr. Galton's law, the immediate parents, 

 on an average, only actually provide half of the units 

 composing the new cell, the other half being provided 

 indirectly by the ancestors. But evidently the extent to 

 which the immediate ancestors are represented in the new 

 cell (out of which the new individual is eventually formed) 

 will, other things being eqaal, depend on how much the 

 individuals (parents) from which the cells came essentially 

 agree with each other. If alike and closely related the 

 immediate parents might be represented by more than 

 half the units ; if unlike and unrelated, by considerably 

 less than half the units in the new cell — the potential 

 new individual. If one parent happened to be prepotent 

 and the other not, only one of the parents might pre- 

 dominate in the new individual. 



From what has been said it will be evident that quite 

 a number of results may follow the union of two germ- 

 cells. Under certain conditions a considerable departure 

 nniy be made in one or more directions, and lead to the 

 appearance of something strikingly new, i. e. to the ap- 

 pearance of a sport. Instead of marked progress, there 

 may be marked retrogression towards a remote ancestor. 

 This when the units repel rather than attract each other, 

 or unite to form unstable and short-lived combinations. 

 As a rule, however, the result is neither a marked step 

 in a new direction nor a long step in a backward direc- 

 tion. There is often slight progress in one or more 

 directions, i. e. normal or continuous variation, accom- 

 panied by slight regression in others. 



Instances of regression we have (1) in the case of the 

 last Iceland foal, which is an exact reproduction of the 

 mother ; * (2) in the Angora rabbit, which is a restoration 



* Tiiis might be either considered an example of prepotency or re- 

 gression to the mother's ancestors. 



