560 J. T. PATTERSON 
INTRODUCTION 
The development of more than one individual from a single egg 
while not a rare phenomenon among animals, is nevertheless of 
much biological interest. It has become customary to classify 
such types of development as asexual or agamic reproduction; but 
obviously this term has come to include a variety of developmental 
phenomena, which are exhibited in animals ranging from the 
Protozoa to the mammals. Among the more common types of 
agamic reproduction are ordinary binary fission, budding, cyclical 
parthenogenesis, paedogenesis, and polyembryony. 
Upon the basis of certain evidence which has been brought for- 
ward from a study of comparatively late embryonic stages, it has 
been correctly concluded that the type of agamogenesis which has 
become habitual in the Texas armadillo is that of polyembryony; 
but so far no one has succeeded in demonstrating the validity of 
this conclusion. The writer has in his possession a series of young 
stages which covers the period of early embryonic differentiation, 
and which represents the material upon which this paper is based. 
An outline of the more general features of the work has already 
been given in a preliminary paper (Patterson ’12). The facts to 
be presented in detail are not without a certain interest and 
significance, not only because they raise to the dignity of an ob- 
served fact the claim for polyembryonic development in the arma- 
dillo, but also for the reason that they throw a great deal of light 
upon related phenomena in other mammals. It is unusual to find 
agamic reproduction in the highest class of animals, and a detailed 
study of the history of this process is greatly to be desired. Fur- 
thermore, there has been considerable speculation as to how ‘iden- 
tical twins’ and similar types of development have arisen, and I 
believe that these studies on the development of the armadillo 
will at least indicate how these phenomena may have comeabout.? 
2 It is a pleasure to acknowledge here my indebtedness to my friend Mr. F. L. 
Whitney of the School of Geology for his able assistance in connection with the 
photographic work. I am also grateful to Mr. F. Pfeiffer, who has greatly facili- 
tated this work by his many successful efforts in obtaining material. 
