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 larvae. 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 larvae, 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 



