1C 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 
nowr 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