The next point which I shall mention in illustration of the extremely close resemblance between certain twins is the similarity in the association of their ideas.  No less than eleven out of the thirty-five cases testify to this.  They make the same remarks on the same occasion, begin singing the same song at the same moment, and so on; or one would commence a sentence, and the other would finish it.  An observant friend graphically described to me the effect produced on her by two such twins whom she had met casually.  She said:  “Their teeth grew alike, they spoke alike and together, and said the same things, and seemed just like one person.”  One of the most curious anecdotes that I have received concerning this similarity of ideas was that one twin, A, who happened to be at a town in Scotland, bought a set of champagne glasses which caught his attention, as a surprise for his brother B; while, at the same time, B, being in England, bought a similar set of precisely the same pattern as a surprise for A. Other anecdotes of a like kind have reached me about these twins.

The last point to which I shall allude regards the tastes and dispositions of the thirty-five pairs of twins.  In sixteen cases—­that is, in nearly one-half of them—­these were described as closely similar; in the remaining nineteen they were much alike, but subject to certain named differences.  These differences belonged almost wholly to such groups of qualities as these:  The one was the more vigorous, fearless, energetic; the other was gentle, clinging, and timid; or the one was more ardent, the other more calm and placid; or again, the one was the more independent, original, and self-contained; the other the more generous, hasty, and vivacious.  In short, the difference was that of intensity or energy in one or other of its protean forms; it did not extend more deeply into the structure of the characters.  The more vivacious might be subdued by ill health, until he assumed the character of the other; or the latter might be raised by excellent health to that of the former.  The difference was in the key-note, not in the melody.

It follows from what has been said 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?