430 E. I. WERBER 



germs has sustained much greater injury than the other, the 

 end-product of further cfevelopment will be a more or less well 

 formed (sometimes even much deformed) embryo (the 'auto- 

 site') with a sort of 'parasitic appendage'-- the 'parasite.' 19 

 This conception of the manner of formation of the 'parasitic' 

 duplicities differs essentially from Wilder's ('08, pp. 363-364, 

 ff.), for no resort is made to the improbable secondary degenera- 

 tion of one (whole) of the already formed components of the 

 diplopagus owing to — what briefly may be called — physiolog- 

 ical dominance of the other component. 20 



It may now be questioned in how far our conclusions regard- 

 ing the origin of the duplicities in our experiments can be ex- 

 tended to those occurring in nature in other vertebrates and 

 particularly in mammals. "While I am, of course, disinclined 

 to do so unconditionally, I think that with some restrictions 

 this extension may be regarded as permissible. For the oft- 

 assumed possibility, if not probability, that in nature, too, the 

 primary causal agent of atypical development is a chemical 

 one (probably due to some disturbances of metabolism during 

 which substances are produced by the body otherwise foreign 

 to it) can not be denied. The human organism — and possibly 

 that may apply to other mammals and to Sauropsidae as well — 

 is subject to disturbances of metabolism of both a serious and 

 a relatively harmless nature. To the former may be counted 

 nephritis, diabetes, jaundice and other diseases of metabolism, 

 while as a relatively harmless, temporary disturbance of metab- 

 olism may be viewed the presence in the organism of certain 

 substances of fatigue after muscular exertion (for instance, lactic 

 acid or monopotassium phosphate) and perhaps some other prod- 

 ucts of transitory abnormal conditions. While the substances 

 of the former owing to their continued more or less severe 



19 Fischel (I.e., p. 290) also suggests that these 'parasitische Anhange' de- 

 velop from primarily rudimentary anlagen. 



20 The differences between the 'parasitic appendages' and the foetal inclu- 

 sions ('teratomata', 'embryomata', etc.) I regard, with Fischel, (I.e., pp. 290- 

 299 ff) as secondary only. A discussion of this subject is deferred to a future 

 publication. 



