of the organism from which these portions have
been detached. And so far does this go, that some experimentalists have
carefully examined the lower orders of animals,--among them the
Abbe Spallanzani, who made a number of experiments upon snails and
salamanders,--and have found that they might mutilate them to an
incredible extent; that you might cut off the jaw or the greater part
of the head, or the leg or the tail, and repeat the experiment several
times, perhaps, cutting off the same member again and again; and yet
each of those types would be reproduced according to the primitive type:
nature making no mistake, never putting on a fresh kind of leg, or head,
or tail, but always tending to repeat and to return to the primitive
type.

It is the same in sexual reproduction: it is a matter of perfectly
common experience, that the tendency on the part of the offspring always
is, speaking broadly, to reproduce the form of the parents. The
proverb has it that the thistle does not bring forth grapes; so, among
ourselves, there is always a likeness, more or less marked and distinct,
between children and their parents. That is a matter of familiar and
ordinary observation. We notice the same thing occurring in the cases
of the domestic animals--dogs, for instance, and their offspring. In
all these cases of propagation and perpetuation, there seems to be
a tendency in the offspring to take the characters of the parental
organisms. To that tendency a special name is given--it is called
'Atavism', it expresses this tendency to revert to the ancestral type,
and comes from the Latin word 'atavus', ancestor.

Well, this 'Atavism' which I shall speak of, is, as I said before, one
of the most marked and striking tendencies of organic beings; but, side
by side with this hereditary tendency there is an equally distinct and
remarkable tendency to variation. The tendency to reproduce the original
stock has, as it were, its limits, and side by side with it there is a
tendency to vary in certain directions, as if there were two opposing
powers working upon the organic being, one tending to take it in a
straight line, and the other tending to make it diverge from that
straight line, first to one side and then to the other.

So that you see these two tendencies need not precisely contradict one
another, as the ultimate result may not always be very remote from what
would have been the case if the line had been quite straight.

This tend