224 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



latter. In all probability we have therefore in these cases to deal with a result 

 similar to that found in lumbricidae ; heterotransplantation may succeed, yet 

 heterodifferentials do exist and exert a certain influence, on the fate of the 

 transplants. On the other hand, we must always consider the possibility that 

 whenever negative results were obtained in heterotransplantations, this may 

 have been due not to a primary incompatibility of the organismal differentials, 

 but to secondary factors, as for instance, to differences in the size of the 

 pieces to be united and to similar more or less accidental conditions. 



The subsequent experiments of Meisenheimer also make it probable that 

 heterodifferentials may play a role in these transplantations. In Lymantria 

 this investigator succeeded in. transplanting ovaries into individuals of the 

 same, as well as of different species, provided the latter were nearly related. 

 We might then conclude that heterodifferentials become manifest only in the 

 case of more distant species, either because in more nearly related species the 

 less marked differences in genetic constitution do not lead to the production 

 of antagonistic mechanisms to the same extent as greater differences, or be- 

 cause the sensitiveness and reactivity to the injurious action of the correspond- 

 ing heterodifferentials are less pronounced in these lower forms than in 

 higher organisms. However, the experiments of Kopec, which followed those 

 of Meisenheimer, indicate that heterodifferentials are well developed in 

 moths; he found that, while homoiotransplantation of sex glands succeeds, 

 heterotransplantation does not. Of interest is also his observation that differ- 

 ent tissues show different degrees of resistance to the manifestation of 

 heterodifferentials ; thus the germ cells are the most sensitive ; these die earliest 

 after heterotransplantation, while transplanted connective tissue grows at first 

 and is only secondarily destroyed. Furthermore, he also notes that the destruc- 

 tion of the transplants takes place the more rapidly, the more distant the 

 heterogenous species are from each other. It seems, then, that in these cases 

 we have to deal with a direct injurious action of heterotoxins ; but in addition 

 cellular mechanisms participate in these processes, inasmuch as phagocytic 

 cells of the host may destroy isolated heterogenous germ cells. 



In insects, according to E. Ries, it is possible to transplant larval fat tissue 

 which has been transformed into a mycetoma, into larvae of different orders. 

 Accordingly, if transplanted from Periplaneta into the peritoneal cavity of 

 Tenebrio, or from Psylla to Tenebrio, the grafted fat tissue remains alive 

 throughout the life of the larva; however, as a result of the strangeness of 

 the transplant, lymphocytes soon begin to collect around it. The transplanted 

 tissue can even survive the metamorphosis of the host into a pupa without 

 being affected by the general changes, and not even by the histolytic processes 

 which occur during this period. In evaluating these observations we must, 

 however, consider the fact that in all the transplantations in insects discussed 

 so far, we have to deal with transplantations not in adult forms, but in cater- 

 pillars and pupae. 



Some remarkable successes in transplantation have been reported by W. 

 Finkler. According to this author, it is possible in the insect species Hydro- 

 philus to replace the head which has been cut off, by grafting the head of 



