16 NATURAL INHERITANCE. [chap. 



are injected, none of the fluid enters those of the 

 mother. Again, not only is the unborn child a sepa- 

 rate animal from its mother, that obtains its air and 

 nourishment from her purely through soakage, but its 

 constituent elements are of very much less recent 

 growth than is popularly supposed. The ovary of 

 the mother is as old as the mother herself; it was well 

 developed in her own embryonic state. The ova it con- 

 tains in her adult life were actually or potentially present 

 before she was born, and they grew as she grew. There 

 is more reason to look on them as collateral with the 

 mother, than as parts of the mother. The same may 

 be said with little reservation concerning the male 

 elements. It is therefore extremely difficult to see 

 how acquired faculties can be inherited by the children. 

 It would be less difficult to conceive of their inheritance 

 by the grandchildren. Well devised experiment into 

 the limits of the power of inheriting acquired faculties 

 and mutilations, whether in plants or animals, is one of 

 the present desiderata in hereditary science. Fortunately 

 for us, our ignorance of the subject will not introduce 

 any special difficulty in the inquiry on which we are 

 now engaged. 



Variety of Petty Influences. — The incalculable number 

 of petty accidents that concur to produce variability 

 among brothers, make it impossible to predict the 

 exact qualities of any individual from hereditary data. 

 But we may predict average results with great cer- 

 tainty, as will be seen further on, and we can also 



