POLYEMBRYONIC DEVELOPMENT IN TATUSIA 633 
In the armadillo the facts of development which we have pre- 
sented in the descriptive part of this paper are fully in accord 
with the theory of budding. We have seen that the early phases 
of differentiation are similar to those of other mammals in which 
the ovum produces but one embryo. Prior to the appearance of 
the embryos, the ectoderm, the entoderm, and the exocoelomic 
mesoderm are differentiated, and later all three of these layers are 
concerned in the formation of the embryonic buds. The initial 
step in budding apparently occurs in the embryonic ectoderm, but 
the entodermal layer is soon involved in the process. It is there- 
fore entirely correct to say that the seat of budding in the arma- 
dillo is to be found in the blastoderm, that is, the blastoderm in 
the budding organ. It may be possible to extend this same con- 
ception to accidental or sporadic cases of polyembryony occurring 
in the lower forms which lay yolk-laden eggs. 
The most important point brought out in this study is the fact 
that polyembryonic development in the armadillo can be inter- 
preted as a type of budding; and, while to show that polyembry- 
ony is a budding process does not solve the question as to the 
determining cause of the division of the blastoderm, yet it is a 
distinct step toward the solution of that important problem. 
It is perhaps premature to attempt an explanation of the ulti- 
mate cause of polyembryony. We first need a comprehensive 
study of each of the forms in which it occurs. Such investiga- 
tions, followed by well-directed experiments, may yield results 
that will reveal at least some of the factors which control poly- 
embryonic development. At present only a few suggestions 
need be made; and, first, we may briefly consider the ideas that 
have been expressed by some of those who have worked on the 
subject. 
Harmer (793), in his excellent paper on embryonic fission in 
Bryozoa, points out several interesting comparisons that can be 
drawn between the process of multiple-embryo formation in 
Crisia and budding in many other organisms. He calls atten- 
tion to the fact that, in at least some of these forms, embryonic 
fission is connected with the deviation from the normal type of 
