INDIVIDUALITY OF EMBRYONAL TISSUES 239 



have given consideration to the influence of organismal differentials in their 

 transplantations. 



More definite is the difference in effects which is seen between homoio- 

 and heterotransplantation. After the latter, there may take place neither a 

 primary nor a secondary unification of the two organisms. The incompati- 

 bility may manifest itself at the surfaces where the organisms are joined 

 together and thus a separation, due to disagglutination, may occur after 

 apparently a primary union of the organisms had taken place. If we unite two 

 distant species, either this latter process occurs or there may be from the 

 beginning a lack of union. If, however, we combine more nearly related 

 species, the two organisms may remain united for a longer period of time, 

 but secondarily also here abnormalities occur, such as a slowing-up of the 

 developmental processes, until they cease in the end altogether. In still other 

 cases more localized abnormalities in development take place, affecting either 

 one or both of the partners ; or on the other hand, disintegration or atrophy 

 of tissues has been observed and at last one partner may be destroyed or 

 incorporated into the dominating one. In these instances we have, therefore, 

 presumably to deal with heterotoxins injuring especially the weaker organism. 

 However, the difficulties experienced in transplantations between different 

 species may depend not entirely on the incompatibilities between the organis- 

 mal differentials as such, but also on secondary factors of a less specific 

 character, such as differences in the size and rate of development of the two 

 partners; factors of this kind may determine the readiness with which two 

 relatively nearly related species can be joined together. 



Of great interest is the observation that in heterotransplantation, if a part 

 of one of the two component organisms disintegrates, the remaining part of 

 this organism may be changed in its development under the influence of cer- 

 tain organs of the other partner, which has now become the dominating factor. 

 Thus, a line of ciliated cells may form in the injured component of the com- 

 bination, when similar developmental processes take place in the dominating 

 component. In such a case we have apparently to deal with an organizer action 

 similar to those actions which are potent during the normal development of 

 embryos, or which may be produced experimentally through implantation 

 of certain specific parts of another embryo, which function as organizers. 

 Evidently the presence of heterodifferentials does not necessarily prevent 

 organizer action. 



We see, then, that in the case of invertebrate embryos a distinct sensitive- 

 ness to heterogenous organismal differentials exists, while a like sensitiveness 

 to homoiogenous organismal differentials is apparently lacking, and in this 

 respect eggs and embryos behave in a similar way to parts of adult inverte- 

 brates when they are joined together. However, as stated above, it may be that 

 what has been interpreted in these experiments as homoiotransplantations, 

 really represented syngenesiotransplantations, since this distinction was not 

 always made by the investigator. 



We shall cite a few experiments which will illustrate some of the general 

 conclusions at which we have arrived and which will bring out some addi- 



