POLYEMBRYONIC DEVELOPMENT IN TATUSIA 631 
in these forms develops essentially in the same manner as though 
producing a part of the whole embryo. 
It is not intended to deny that influences of a mechanical nature 
may not, in certain cases, lie at the basis of multiple-embryo 
formation. Any one advocating such a theory may bring to 
his support not only the facts of artificial blastotomy, but also 
those derived from experimental studies on later development, 
like those of the pioneer work of Haeckel (’69) on the blastulae 
of Crystallodes and of the more recent and well-known studies 
of Spemann (’01, ’03) on the triton egg. This rather simple 
mechanical or semi-mechanical explanation might hold in the 
sporadic cases of polyembryony, like those of duplicate twins 
and double monsters, but what evidence have we that blastotomy 
operates in the case of specific polyembryony in higher forms? 
As yet we know very little about the details of the early develop- 
ment in such cases. It is a significant fact that such evidence 
as we do possess does not support the theory, and it is certainly 
true that these studies on the armadillo—a form in which we 
have a most striking case of specific polyembryony—have not 
revealed any evidence which tends to support the blastotomy 
theory. On the contrary, the evidence points unmistakably to 
a different explanation, namely, that a type of budding lies at 
the basis of polyembryony in this form. 
c. The theory of budding. The process of budding is a very 
common method of reproduction among organisms. In plants 
it is practically universal, and in animals it is frequently met with, 
especially among the lower forms. In many cases asexual repro- 
duction by budding occurs late in the life cycle, as for example 
among coelenterates. In such forms as the common Hydra it 
is customary to regard the organism as an adult when budding 
begins. But the appearance of budding is by no means confined 
to adult organisms, or even to late stages of development, for it 
may appear very early in the life cycle. 
9 The term ‘spontaneous blastotomy’ has been used by Bugnion and Marchel 
to describe the process of polyembryony in the parasitic Hymenoptera, but not 
in the sense that each embryo can be traced to a single blastomere. Brandes (’98) 
has suggested the term ‘Germmogonie’ in lieu of polyembryony. 
