HYBRIDIZATION AND TRANSPLANTATION 327 



is concerned. He made still finer gradations in accordance with Poll's ter- 

 minology, distinguishing between tokonoth hybrids, which are fertile, and 

 steironoth hybrids, which are sterile ; the disharmony in the constitution of 

 the parent strains giving rise to the former, should be less than that giving 

 rise to the latter. Accordingly, he finds that exchange of tissues between 

 species with tokonoth hybrids gives the better results. We shall first cite 

 certain examples of Schultz's observations and then discuss some of the 

 factors complicating his transplantations. Such a discussion will provide an 

 opportunity to state also some of the principles which apply to transplantation 

 in general. 



I. Experiments in Amphibia. Skin of Bufo vulgaris transplanted to Bufo 

 viridis remained alive one hundred days, and the reciprocal transplant, fifteen 

 to thirty days ; these two species can be hybridized. Skin grafted from Rana 

 temporaria to Rana arvalis lived eighty days, the reciprocal transplant, one 

 hundred days. In these cases in which the skin was exchanged between hy- 

 bridizable species the results were therefore relatively good. On the other 

 hand, skin transplanted from Hyla arborea to Rana esculenta remained alive 

 only ten to twenty days. These two species not being hybridizable, the life 

 of the transplant was shorter. However, also transplantation of skin from 

 Rana temporaria to Rana esculenta may give very good results and the graft 

 may remain alive for more than one hundred days, although these two species 

 are not hybridizable. Exchange of tissues between urodele and anuran am- 

 phibia was unsuccessful. 



The principal results obtained by Schultz in the heterotransplantation of 

 amphibian skin may be summarized as follows : Length of time during which 

 transplants remained alive after: (a) Transplantation of skin between hybrid- 

 izable species. 

 Exchange of tissues between Rana temporaria and Rana arvalis : 



70 to 105 days. 

 Transplantation from Bufo vulgaris to Bufo viridis : 100 days. 



From Bufo viridis to Bufo vulgaris : 15 to 30 days. 

 (b) Transplantation of skin between non-hybridicable species. 



From Bufo viridis to Rana esculenta : 10 to 20 days. 



From Hyla to Rana: early death of host as well as of transplant. 



From Rana esculenta to Rana temporaria : 40 days. 



From Rana temporaria to Rana esculenta: 130 days. 



From Salamander to Rana esculenta : 8 to 10 days. 

 It is evident that there is no complete correspondence between compatibility 

 of host and transplant and hybridizability. It is furthermore probable that 

 toxic actions, due to other factors than organismal differentials, play a role, 

 at least in some of these transplantations. 



II. Experiments in Birds. Schultz finds that the skin of the canary when 

 transplanted to hybridizable species remains alive up to twenty-five days and 

 during that time shows mitoses, whereas after transplantation to the pigeon, 

 with which the canary is not hybridizable, the skin is found necrotic after 

 seventeen days. Skin exchanged between pigeon and laughing dove, which 

 are hybridizable, remains alive up to thirty days, during which time mitoses 



