Harris Ha^^-thorne Wilder 423 



Another form of the theory of superfluity is that of Windle, 93, who, 

 quoting Sutton, compares the production of a double monster to " the 

 same tendency which causes dichotomy of the ray in star-fish, or digits 

 in mammals, a tendency which, should it affect the axis of the embryo, 

 will lead to the production of duplex monsters of varying development 

 and different degrees of union, or even result in viable twins." He 

 adds : " This statement, so far as it goes, concisely states the view which 

 I hold on the subject."' In his summary he gives as the ultimate cause 

 for this dichotomy a superfluity of germ plasm existing in the germ." 

 This superfluity may be the result of (1) a faulty segmentation of the 

 polar bodies, (2) a faulty formation of the spermatozoon, or (3) poly- 

 spermy. His statement that this superfluity in true double monsters 

 leads to a fission " prior to that by which normal development is com- 

 menced " is practically an expression of the theory of the partial or 

 total fission of the first two blastomeres, as advocated in the present 

 paper, with the interesting addition of a possil)le cause for the phe- 

 nomenon. He causes some confusion, however, in attempting to bring 

 into the same category all cases of minor duplicity, such as hyperdac- 

 tylism, and by asserting that there is " no gap " between such cases and 

 true double monsters. 



Y. — As representative of the fusion theory, by which tvro original 

 embrj^os become a composite monster by atrophy of certain parts, we 

 may cite Panum, who holds that all cases involving the doubling of 

 trunJc and limbs presuppose two fetuses, originally with a completely or 

 partially double axial anlage, one-half of which has become atrophied 

 during the course of development. He acknowledges, however, that 

 many cases of minor duplicity may be the result of budding. 



VI. — A unique theory is that of postregexeeation, recently brought 

 forward by Tornier, 97-01, to explain cases of minor duplicity and later 

 extended so as to include all cases of compound monsters. Tornier has 

 studied experimentally certain of the well-known cases of regeneration 

 found among lower animals, such as the tails of lizards, the limbs of 

 salamanders, etc., and has shown that while a complete loss of the mem- 

 ber will resul.t in a simple regeneration of the part, yet that a certain 

 kind of wound, made in the place where the loss usually occurs, yet 

 insufficient to cause the loss of the part, will occasion the growth of a 

 new member in the same manner as though the original had been actually 

 'lost, thus producing duplicity. From this he holds that, while such 

 phenomena may occur after birth in certain of the lower animals only, 

 thev vet may occur before birth, in birds and mammals, as a result of a 

 lesion affecting the fetus. This seems a reasonable theorv when con- 



