concerning the similar
dispositions of the twins, the similarity in the associations of
their ideas, of their special ailments, and of their illnesses
generally, that the resemblances are not superficial, but extremely
intimate. I have only two cases of a strong bodily resemblance being
accompanied by mental diversity, and one case only of the converse
kind. It must be remembered that the conditions which govern extreme
likeness between twins are not the same as those between ordinary
brothers and sisters, and that it would be incorrect to conclude
from what has just been said about the twins that mental and bodily
likeness are invariably co-ordinate, such being by no means the case.

We are now in a position to understand that the phrase "close
similarity" is no exaggeration, and to realise the value of the
evidence I am about to adduce. Here are thirty-five cases of twins
who were "closely alike" in body and mind when they were young, and
who have been reared exactly alike up to their early manhood and
womanhood. Since then the conditions of their lives have changed;
what change of Nurture has produced the most variation?

It was with no little interest that I searched the records of the
thirty-five cases for an answer; and they gave an answer that was
not altogether direct, but it was distinct, and not at all what I
had expected. They showed me that in some cases the resemblance of
body and mind had continued unaltered up to old age, notwithstanding
very different conditions of life; and they showed in the other
cases that the parents ascribed such dissimilarity as there was,
wholly or almost wholly to some form of illness. In four cases it
was scarlet fever; in a fifth, typhus; in a sixth, a slight effect
was ascribed to a nervous fever; in a seventh it was the effect of
an Indian climate; in an eighth, an illness (unnamed) of nine
months' duration; in a ninth, varicose veins; in a tenth, a bad
fracture of the leg, which prevented all active exercise afterwards;
and there were three additional instances of undefined forms of ill
health. It will be sufficient to quote one of the returns; in this
the father writes:

"At birth they were _exactly_ alike, except that one was born with a
bad varicose affection, the effect of which had been to prevent any
violent exercise, such as dancing or running, and, as she has grown
older, to make her more serious and thoughtful. Had it not been for
this infirmity, I think the tw