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. 9 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 \iery 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 'Germ'mogonie' in lieu of polyembryony. 



