250 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



generative tissues can develop in accordance with the potentialities of the 

 transplants. It seems, then, that too slight a differentiation of the trans- 

 planted tissue favors its complete adaptation to the host and is responsible for 

 the lack of a growth momentum, which would otherwise have led the trans- 

 plant to develop in its own way. 



We shall consider transplantations in their relations to organismal and 

 organ differentials still further in the following chapter, in which we analyze 

 organizer actions and their connection with organismal differentials. But the 

 data which we have already discussed lead to the conclusion that the outcome 

 of transplantations in amphibia depends primarily upon two sets of consti- 

 tutional factors, namely, (1) the phylogenetic stage of development; this, in 

 urodeles, is more primitive, the precursors of the organismal differentials are, 

 as yet, less differentiated and, therefore, the range of relationship in which 

 transplantation of embryonal material succeeds is wider than it is in anuran 

 amphibia. (2) The ontogenetic stage of development of the organismal differ- 

 entials ; the genes from which the organismal differentials develop are fixed 

 for each species and individual, and they remain unchanged in all the tissues 

 throughout embryonal development. In contrast to this fixity of the genes, the 

 degree of differentiation which the organismal differentials have reached in 

 successive stages of embryonal development differs; the greater the tissue 

 and organ differentiation, the further advanced is also the differentiation of 

 the organismal differentials, and correspondingly, the narrower will be the 

 range of relationship within which the transplantations succeed. Besides, in the 

 same embryonal stage different tissues and cells may differ as to the degree 

 of differentiation they have attained, and, correspondingly, they may differ 

 also as to the stage of transformation of the gene-precursors into the actual 

 organismal differentials, which are localized in these tissues. Since organismal 

 and also organ differentials are further differentiated and more fixed in 

 anuran larvae than in urodeles at corresponding stages of embryonal de- 

 velopment, the transplantability of the former will be less than that of the 

 latter at any given period. 



Furthermore, during regenerative newformation of limbs, conditions exist 

 which in certain respects resemble those present during embryonal develop- 

 ment (Schaxel) ; a graded differentiation of the regenerating tissues and a 

 corresponding maturation of the organismal differentials take place. There- 

 fore, if buds of extremities representing early stages of regeneration are 

 transplanted, they may give origin to mixtures of various tissues ; but if 

 somewhat later stages are transplanted the tissues are fixed in their poten- 

 tialities and in the localization of the regenerating material and under these 

 conditions typical limbs develop. The great plasticity of the blastema of limb 

 or tail of an amphibian is demonstrated in a remarkable experiment of 

 Schotte, in which he showed that after transplantation into the eye of frog 

 larvae, from which the lens had previously been removed, the blastema 

 changed into lens tissue under the influence of organizers located in the 

 eye of the host. 



Durken and Kusche diminished the effect of the host tissue on the trans- 



