‘THE BIOLOGY OF TWINS 159 
of the armadillo rolling up into a ball (a pre- 
rogative of the Little Armadillo) “are totally in- 
applicable to this species, for the animal turns over 
on its back and kicks viciously and effectively with 
its powerful and heavily armed feet.” But beyond 
noting that the young ones are born well advanced 
and able to walk about within the first few hours, 
we must not say anything more about the natural 
history of the Nine-banded Armadillo. For our 
present purpose the important fact is that this quaint 
creature normally and habitually produces quad- 
ruplets—a remarkable fact which several zoologists 
have studied, and Mr. Newman most thoroughly 
of all. 
Many mammals, such as_ rabbits, produce 
numerous young ones at once, but each of these 
develops separately from an egg-cell, and the 
phenomenon of multiparous birth has nothing to do 
with twinning. That term is appropriate when 
a creature normally uniparous, such as cow or bat, 
gives birth simultaneously to two offspring. As 
every one knows, these may be quite dissimilar, or 
they may be living images of one another, in which 
case they are always of the same sex. In un- 
toward cases twins may be physically continuous, 
as in the “ Siamese twins,’’ and one member of the 
pair may be to a varied degree degenerate or un- 
developed,—the result being the twin-monsters of 
the show or of the embryological museum. Some 
of them are the results of fission, others of fusion. 
But there has been much vagueness and uncertainty 
