642 J. T. PATTERSON 



As to the origin of duplicate twins, Wilder advocates the 

 blastotomy theory, believing that it is the result of a total sepa- 

 ration of the first two blastomeres of the single egg. In case the 

 blastomeres fail to separate completely, symmetrical double 

 monsters (dislopagi) result. In this connection he says, "The 

 double monsters of which we have authentic record are sufficiently 

 numerous and diverse to represent every stage from that of the 

 otherwise normal individual with a doubling of certain of the 

 median parts, to that of two complete duplicate twins with a 

 slight connection between them." 14 Finally, be believes that 

 unequal duplicate monsters (autosite and parasite) are the result 

 of a secondary fusion (due to the great contiguity) of two embryos 

 which were at first duplicate twins. 



The contention that duplicate twins and double monsters arise 

 from a single egg is undoubtedly sound, but* the conclusion that 

 their origin is the result of a complete or a partial separation of the 

 first two blastomeres, is, I believe, open to question. However, 

 in the absence of any study in the early stages of these sporadic 

 cases of polyembryony, and in view of the results from experiments 

 on artificial blastotomy, this conclusion seemed both natural 

 and logical. In the s-tudy of the embryology of the armadillo we 

 have a most excellent opportunity to put the blastotomy theory 

 to test; for here is a mammal with a simplex type of uterus, and 

 one which habitually reproduces by polyembryony. I am there- 

 fore bold enough to suggest that the conclusions which I have 

 drawn concerning the origin of the embryos in this mammal may 

 also apply to cases of duplicate twins and double monsters in the 

 human species. And I am encouraged to make this suggestion be- 

 cause of the recent discoveries in the human ovum (e. g. the Bryce 

 and Teacher ovum, '08), in which the condition of the ectodermal 

 vesicle is shown to be such as to require no great stretch of the 

 imagination to picture how diverticula might arise from it, and 

 thus initiate the development of two or more embryos. Nor is 

 there any greater mental strain in accounting for the origin of 

 composite monsters in this way than is required in the hypothet- 



14 Loc. cit., p. 462. 



