Chap. XIII. 
EMBRYOLOGY. 
443 
fancy animals^ cannot positively tell, until some time 
after the animal has been born, what its merits or form 
will ultimately turn out. We see this plainly in our own 
children; we cannot always tell whether the child will 
be tall or short, or what its precise features will be. ‘ The 
question is not, at what period of life any variation has 
been caused, but at what period it is fully displayed. 
The cause may have acted, and I believe generally has 
acted, even before the embryo is formed; and the varia»“ 
tion may be due to the male and female sexual elements 
having been affected by the conditions to which either 
parent, or their ancestors, have been exposed. Never¬ 
theless an effect thus caused at a very early period, even 
before the formation of the embryo, may appear late in 
life; as when an hereditary disease, which appears in 
old age alone, has been communicated to the offspring 
from the reproductive element of one parent. Or 
again, as when the horns of cross-bred cattle have been 
affected by the shape of the horns of either parent. For 
the welfare of a very young animal, as long as it remains 
in its mother’s womb, or in the egg, or as long as it is 
nourished and protected by its parent, it must be quite 
unimportant whether most of its characters are fully 
acquired a little earlier or later in life. It would 
not signify, for instance, to a bird which obtained its 
food best by having a long beak, whether or not it 
assumed a beak of this particular length, as long as it 
was fed by its parents. Hence, I conclude, that it is 
quite possible, that each of the many successive modi¬ 
fications, by which each species has acquired its pre¬ 
sent structure, may have supervened at a not very 
early period of life; and some direct evidence from our 
domestic animals supports this view. But in other cases 
it is quite possible that each successive modification, or 
