TRANSPLANTATION AND I INDIVIDUALITY. 167 



cially the grafting of amphibian embryos, a method originated by 

 Born and subsequently used by Braus, Harrison and others, is 

 interesting in this connection; furthermore the transplantation of 

 skin (Lewis, Weigl), of the eye (Uhlenbath) and the experi- 

 ments of Spemann add valuable data. There is apparently no 

 difference between the results of auto- and homoiotransplanta- 

 tions. On the other hand a heteroreaction again exists, but is less 

 marked than in the case of higher veretebrates. Transplantation 

 into nearer related species succeeds better than into further dis- 

 tant species. 



In adult amphibia we find the first indication of the existence 

 of a homoiodifferential. However, in adult fishes and amphibia 

 the reaction against homoiotransplantation seems to be less 

 marked than in adult mammals and birds, although we must con- 

 fess the evidence concerning the fate of homoiotransplanted 

 tissues in these classes appears somewhat contradictory. We have 

 furthermore to consider the difference in temperature at which 

 reactions occur in lower and higher vertebrates. This factor 

 might render the homoio reaction much slower in amphibia. 

 Despite these difficulties we may provisionally conclude that the 

 reaction against homoio and heterodifferentials is somewhat less 

 pronounced in lower than in higher vertebrates. 



The interesting observations of Murphy and Rons who made 

 successful heterografts of tumors in the allantois of chick em- 

 bryos suggest that the individuality reaction is absent even in the 

 embryo of higher vertebrates which serve as hosts. This agrees 

 with an observation of Braus which seems to indicate that in am- 

 phibian larvae used as hosts the heteroreaction appears at a cer- 

 tain stage, namely, when the circulation has been established in 

 the transplant. Likewise if we transplant embryonic mammalian 

 tisue into adult hosts the homoioreaction seems to be somewhat 

 elss pronounced in the case of certain tissues ; the reaction, how- 

 ever, does exist. Embryonic mammalian tissues call forth a very 

 rapid heteroreaction in adult hosts (Saltykow). 



To summarize, we find absence of homoioreaction in inverte- 

 brates and larvae of lower vertebrates. The heteroreaction exists 

 here, but is less pronounced. In lower adult vertebrates the 



