222 HARRIS HAWTHORNE WILDER. 



controls the development and eventual arrangement of the 

 parts in question, and I am of the opinion that a carefully estab- 

 lished cell lineage would substantiate the claims of the two 

 authors in 1910, quoted above, or their statement of 1909, "In 

 the case of Dasypus [Tatusia] each embryo probably arises from 

 one of the blastomeres of the four-celled stage," which does not 

 open the question of whether these blastomeres were actually 

 separated from one another or w^ere only the ancestors of the 

 separate embryonal anlages of a later time. Concerning the 

 blastotomy theory, that is, an actual separation of the blasto- 

 meres, I may take this occasion to state that I no longer believe 

 it, since, among other reasons, comes the very cogent one that 

 such a separation in man, or in any mammal, would necessarily 

 produce as many separate and distinct choria, each with its own 

 attachment to the uterus, a condition which is found in fraternal 

 births, each from a separate egg, but never in true polyembryony. 

 In turning to my earlier work, however, I find this theory stated 

 in unequivocal phrase, as "the total separation of the first two 

 blastomeres of a single egg" (1904, p. 462) and I take this op- 

 portunity to recant so far as the "total separation" is concerned, 

 while still adhering to the first two blastomeres as the probable 

 ancestors of the two later embryonal buds respectively. 



While engaged in noting changes of opinion, I may say further 

 that the view of a different origin for double monsters with unequal 

 components, autosite and parasite, which I asserted in my paper of 

 1904, pp. 462-463,'! rejected utterly later on, 1908, p. 362, and con- 

 sidered such cases as in origin exactly like other double monsters 

 (including separate twins), and that the deformed condition had 

 been brought about by some accident which deprived one of the 

 components of either its normal amount of nourishment, or pre- 

 vented a normal growth in some mechanical way. As. my first 

 view only has been quoted by Newman and Patterson this seems 

 to be an instance of the very common case in which an error is 

 published much more widely than its later correction. Such 

 modifications, or flat rejections, of former views are naturally 

 incident to all progressive thinking, and in a subject so complex 

 and so vital as the present investigation are inevitable. 



Concerning the causes which produce a double monster, that 



