630 J. T. PATTERSON 
of investigators, and in the earlier work on this armadillo the same 
view was held. This idea undoubtedly has its inception in, and 
has received most of its support from the results of certain ex- 
perimental studies involving the mechanical or semi-mechanical 
separation of early blastomeres. For it has been demonstrated 
that an early isolated blastomere of the two-celled or four-celled 
stage of the eggs of the echinoderm (Driesch ’92), medusa 
(Zoga 95-6), Amphioxus (Wilson ’93), and teleost (Morgan ’93) 
may develop into a complete but small larva, and even in the egg 
of the amphibian a blastomere of the two-celled stage, under 
certain conditions (Schultze 795, Morgan 795, and Herlitzka ’97) 
may also develop into a complete organism. What then seemed 
more logical then to conclude that in the case of polyembryonic 
development the early blastomeres had in some way become 
displaced or isolated, and that each cell thus separated formed 
the center for a single individual. Moreover, this inference 
seemed all the more plausible in the light of certain studies on 
twins in the human species. Wilder (’04) in particular, in his 
extensive paper on duplicate twins and double monsters, advo- 
cates the theory that each member of a pair is the product of 
one blastomere. 
The evidence that has been presented in the first part of this 
paper makes it certain that polyembryonic development in the 
armadillo cannot be explained on the basis of a spontaneous 
blastotomy, in the sense that each embryo is the lineal descen- 
dant of a single blastomere of the four-celled stage, and it causes 
one to view with some doubt the conclusions of this same nature 
that have been drawn by those who have worked on other poly- 
embryonic forms. In this connection it should be kept in mind 
that, although an equipotentiality seems well established for 
the early blastomeres of the eggs of the echinoderms, medusa, 
amphioxus, teleost, and others, yet there are many forms in 
in which a blastomere does not have the power to develop into 
a whole individual. Crampton (’96) on gasteropods, and Chabry 
(87) and Conklin (’05, ’06) on ascidians have conclusively demon- 
strated that a blastomere of the two-celled or four-celled stage 
