ORIGIN OF MONSTERS. II 413 



grams of the latter demonstrates with almost mathematical 

 precision how the development of any diplopagus may result 

 from the variation in the degree of approximation and the 

 angle of incline of two embryonic primordia. 9 It is not prac- 

 ticable at this place adequately to present Fischel's views. They 

 have, however, been fully discussed by Schwalbe (I.e.) to whom 

 as well as to Fischel's paper the reader must be referred. Here 

 it may suffice to say that his analysis accounts successfully for 

 the morphogenesis of all double monsters, some of which (like 

 the diprosopos, the dicephalos, the catadidymus and the meso- 

 catadidymus) have eluded all other attempts at interpretation. 



However, it must be admitted that absolute proof for all of 

 Fischel's postulates is wanting for vertebrates higher than 

 Petromyzon, since Bataillon. unfortunately, made no obser- 

 vations regarding the morphogenesis of the double embryos he 

 produced by osmotic pressure in Leuciscus. Nor is such proof 

 furnished by the experiments on amphibians (referred to above), 

 as they demonstrate only how certain duplicities may result 

 from the separation of equipotent parts of the egg, but give us 

 no clue regarding the formation of various other duplicities (in 

 other vertebrates) by secondary fusion of duplicated primordia, 

 as assumed by Fischel. 



It may also be mentioned, in passing, that Fischel's theory 

 (blastotomy by osmotic pressure and subsequent chance con- 

 figuration of the duplicated primordia) does not account for the 

 malformations often exhibited by duplicities. The point is 

 not an unimportant one, for as I shall attempt to show, these 

 deformities may often be syngenetic with the doubling of the 

 primordium. Besides, as will be pointed out later, the defor- 

 mities of one or both components of a duplicity give us an im- 

 portant clue to the morphogenesis of the 'parasitic double 

 monsters.' 



9 The various possib.le combinations in man were portrayed very suggestively 

 in the well known diagrams of Wilder ('04) who, however, in his more recent 

 worjv ('08) has abandoned his former views on diplogenesis in favor of his pres- 

 ent 'theory of Cosmobia.' 



