HIGHER INVERTEBRATES AND AMPHIBIA 231 



plantation among anuran species. The center of the graft degenerates first 

 because it is injured by the lack of foodstuffs; it succumbs therefore before 

 the peripheral parts do, which resist the injurious action of the bodyfluids 

 better, since they are near the source of oxygen and the foodstuffs. Careful 

 microscopic studies of grafts in amphibians tend to prove, therefore, that 

 here, in principle, already a fargoing specialization of the organismal differ- 

 entials has taken place and that this specialization manifests itself in a similar 

 manner in amphibia and in mammals. 



In progressing from the urodeles to the anurans there is thus noted an 

 advance in the specificity of the reaction on the part of the host against a 

 strange organismal differential. Furthermore, parallel to this progression in 

 specificity a reverse change takes place in the regenerative and integrative 

 power of these classes of animals. While this is very much more restricted 

 in urodeles than in the primitive invertebrates, still a certain degree of the 

 power of regeneration has been retained by them, as indicated by their ability 

 to regenerate extremities. In the anurans, on the other hand, only the rudi- 

 ments of this integrative power are left, consisting merely in the ability of a 

 number of individual tissues to undergo, to a moderate degree, proliferative 

 processes, which may lead to the filling-out of certain defects and to wound 

 healing in the skin. In accordance with' our previous conclusions we find, 

 therefore, also in this instance a parallelism between the degree of plasticity 

 in the organ-forming potencies of organisms and the development of the 

 finer organismal differentials. The greater the trans formability of organs and 

 the greater the restitutive and integrative power of organisms, the more 

 undifferentiated appear to be the organismal differentials and the less specific 

 are their effects. 



From this brief survey of the behavior of organismal differentials during 

 phylogenetic development we may conclude that already in the most primitive 

 organisms certain reactions against tissues from strange species are present, 

 and that these reactions become more refined and specific with the advance 

 to groups of animals whose structure is more complex. But we observe also 

 that with progressing evolution the differentiation of organs and tissues, their 

 decreasing plasticity and increasing fixity are much more clearly graded than 

 is the refinement of the organismal differentials. No definite advance was 

 observable in the individualization of organismal differentials within the most 

 primitive classes of animals ; they all seemed to behave in a similar manner. 

 However, this lack of steady progression is perhaps only apparent and not 

 real. It may be at least due partly to the method used for the demonstration 

 of the organismal differentials, namely, observation of the reactions which 

 take place in an animal against a strange transplant, or between two partners 

 differing in their organismal differentials; now, in the lowest organisms the 

 tendency to integration is very great and there is the danger that the integra- 

 tive reactions which follow various kinds of disturbances may be interpreted 

 as reactions against strange organismal differentials. Furthermore, we may 

 recall the great complexity of the factors which enter into the reactions against 

 strange organismal differentials, and the fact that the intensity of these reac- 



