THE BIOLOGY OF TWINS 163 
and temperament, intonation and handwriting. 
It may be both interesting and useful to recall some 
of the extraordinary illustrations of the close re- 
semblance of duplicate twins, developed, as the 
armadillo story makes clear, from one egg. Mr. 
Galton tells of a case in which no one, not even the 
twins themselves, could distinguish their hand- 
writing; of another case in which “a doubt re- 
mains whether the children were not changed in 
their bath, and the presumed A is not really B, 
and vice versa”; of two girls who used regularly 
to impose on their music teacher, one of them taking 
two lessons in succession when the other wished 
a whole holiday; of a schoolmaster who, to make 
sure, used to flog both twin-brothers when one had 
sinned; of nine cases where a twin addressed his or 
her reflection in a mirror in the belief that it was the 
other twin in person; of four or five cases of doubt 
during an engagement of marriage; and of a quaint 
interchangeableness of expression, “ that often gave 
to each the effect of being more like his brother 
than himself.” The depth of the constitutional 
sameness is said to be sometimes seen in the twins 
sharing some special ailment at the same time or 
showing the same exceptional peculiarity. ‘‘ Two 
twins,’ Galton noted, ‘at the age of twenty-three 
were attacked by toothache, and the same tooth 
had to be extracted in each case.’ Two closely 
similar twin-brothers, of similar tastes and pro- 
fession, died of Bright’s disease within seven months 
of each other. Sometimes the resemblance is 
