Chapter J 



Transplantation and Individuality of 

 Embryonal Tissues 



We have studied the phylogenetic development of organismal dif- 

 ferentials and their manifestations in animals, using transplantation 

 of adult tissues as indicator. In this and the following chapter we 

 shall study the ontogenetic development of the organismal differentials and 

 for this purpose we shall make use of the data supplied by the transplantation 

 of embryonal tissues. In these experiments either parts of developing organ- 

 isms were joined together, each of which was capable of independent life, or 

 relatively small, not independently viable pieces of embryonal tissues or organs 

 were transplanted into embryonal or adult organisms. The union of inde- 

 pendently viable parts bears some resemblance to parabiosis especially if the 

 size of the surface, by means of which the partners are joined together, is 

 relatively small in comparison with the diameters of the grafts. 



I. Transplantation in Amphibia. It was in amphibia that the possibility of 

 uniting parts of two different embryos into one organism was discovered in 

 1897 by Born, whose work thus introduced a problem which subsequently 

 suggested many similar investigations in amphibia as well as in other classes 

 of animals. 



Born used in his experiments larvae of anuran amphibia. In these as in 

 other transplantations, besides the organismal differentials, other factors, some 

 of which were non-specific, helped to determine the results, and it is im- 

 portant, as far as feasible, to separate these factors. Thus, the rapidity of 

 growth of larvae of Rana esculenta is greater than that of larvae of Rana 

 fusca or arvalis, and in the union of parts of the former with parts of one 

 of the two latter larvae, components of Rana esculenta tend to dominate over 

 the other components and cause their atrophy. It is necessary to distinguish 

 such secondary effects from the direct manifestations of organismal differ- 

 entials, although the growth rate is, of course, as well as all other character- 

 istics of tissues and organs, at least in part, determined also by the genetic 

 constitution of the organism. 



As a direct effect of the organismal differentials, we may consider the 

 readiness with which autotransplantation of embryonal constituents succeeds : 

 two parts can be readily united into a single organism, in which the corre- 

 sponding organs form so perfect a connection that, subsequently, the place 

 of junction can, as a rule, no longer be recognized; however, difficulty may 

 be experienced in the joining together of the components of the chorda dor- 

 salis, especially in older larvae. As in adult annelids, so also in amphibian 

 embryos analogous organs of the partners usually find each other and unite. 



The results of homoiotransplantation are about the same as those of auto- 



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