TRANSPLANTATION AND INDIVIDUALITY. 165 



with the tissue differential, but not with the corresponding dif- 

 ferential in the body fluids. We may designate the substance 

 present in the body fluid and interacting with the individuality 

 and species differential of the tissues as the supplementary indi- 

 viduality and species differential. 



PHYLOGENETIC AND ONTOGENETIC EVOLUTION OF THE INDIVID- 

 UALITY AND SPECIES DIFFERENTIAL. 



The analysis of the individuality differential which we have 

 given so far applies altogether to the higher animals, mammals 

 and birds. Almost all the experiments to which we referred in 

 this paper were made in these two classes. Does this fine differ- 

 entiation of individuality, the delicate discernment of individual 

 relationship such as we have found in the cells and tissues of 

 higher animals, also exist in the lower animals? Is it a charac- 

 teristic of all animal cells or has it gradually evolved together 

 with other differentiations in the course of evolution? Have the 

 differentials, or rather the reactions they call forth, had an evo- 

 lution like structure and certain functions? So far as I am ac- 

 quainted with the literature this question has never been put and 

 no planful investigations have been carried out tending to answer 

 it. In a general way, however, it is known that in lower forms 

 and in earlier embryonic stages transplantability is greater, in 

 correspondence with the greater regenerative power, of these 

 organisms, or in dependence on the greater power of isolated parts 

 of these beings to sustain themselves separated from the remnant 

 of the animal, as particularly W. Schultz has pointed out. But 

 the evolution of species and individuality differentials has not 

 been considered in a conscious way as far as I am aware. 



I have recently studied the literature of transplantation with 

 the view of determining whether the experiments which were 

 carried out by various investigators for the solution of problems 

 of a different character might throw some light on this question. 

 While in some respects I found the evidence here and there some- 

 what contradictory, still I believe that certain conclusions may be 

 arrived at on this basis with a fair degree of certainty. 



To begin with invertebrate embryos, the experiments of 

 Driesch, Morgan, Goldfarb and others show that parts of em- 



