160 SECRETS OF ANIMAL LIFE 
about the whole subject of twinning, and we wel- 
come the light that has come from the armadillo. 
Mr. Newman’s investigations have made it quite 
certain that the quadruplets of the Nine-banded 
‘Armadillo are all simultaneously produced from one 
egg, within a common birth-robe, and that they 
are always of the same sex. In a neighboring 
species, the Hybrid Armadillo, believed to be a 
recent evolutionary derivative of the Nine-banded, 
the number of ‘“‘polyembryonic offspring” devel- 
oped from one egg varies from seven to twelve, 
with a tendency to settle down to eight—a varia- 
bility which suggests that the peculiarity in question 
is of comparatively recent origin. 
When the egg of the lancelet at the two-cell stage 
is shaken vigorously in the sea-water in which it 
floats, the two cells separate and form two half-sized 
embryos and larve. If the shaking is less vigorous, 
so that the two cells do not go apart, Professor 
E. B. Wilson found that Siamese-twin embryos are 
formed. Similarly from the four-cell stage he got 
four dwarf embryos and larve, or queer non-viable 
Siamese quadruplets! In some Ctenophores or 
sea-gooseberries, twinning is often noticed after 
storms, for the first two cells of the segmenting 
egg are shaken apart. But it is not by the disloca- 
tion of the first four cells that the quadruplets of 
the Nine-banded Armadillo arise. What happens 
is that in a single embryonic vesicle formed by the 
segmentation of the fertilized egg-cell, and after 
considerable differentiation has occurred, four 
