246 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



effects, involved, perhaps, in the establishment of connections between the 

 transplants and the central nervous system. 



Graper and Alverdes, on the other hand, find that transplantations of ex- 

 tremity buds from larvae of Rana palustris to Rana sylvatica succeed only 

 temporarily; they retrogress within four to five weeks. Similarly, in earlier 

 experiments Born had observed that transplantation of skin from larvae of 

 Bombinator to Rana did not succeed very well. Likewise, Ekman had noticed 

 that after exchange of gill ectoderm between these organisms the transplants 

 were soon destroyed or cast off. Among amphibian larvae, and especially also 

 in urodele larvae, the transplantations become more difficult if the species 

 used are more distantly related. Thus, Harrison found that the balancer 

 anlage can be readily transplanted from Amblystoma punctatum to Amblys- 

 toma tigrinum, but if this organ is grafted from Amblystoma punctatum to a 

 larva of Rana sylvatica, only a short appendage develops. Similarly, the 

 induction of the balancer in Triton by means of frog material gives only 

 doubtful results (Mangold). An ear vesicle transplanted from a larva of 

 Rana esculenta to Triton taeniatus remained alive at most for twenty-nine 

 days, and in the majority of cases it disappeared even earlier; yet the trans- 

 planted organ, while it lived, was able to induce the formation of cartilage 

 in the host (Balinski). In the tailbud stage of Amblystoma punctatum and 

 tigrinum, pieces of spinal cord can be exchanged between these two species 

 and may remain alive, the brachial plexus growing out from the transplant 

 into the host. However, subsequently irregularities do develop ; there is a 

 greater mortality and metamorphosis does not take place in the bearers of the 

 grafts (Wieman and Nussman). In urodele larvae heterotransplants from 

 nearly related species may not only remain alive, but the tissues from both 

 species may intermingle with each other, so that chimaerae develop. Thus 

 Schaxel grafted parts of regenerative blastemas of extremities of white 

 axolotls into autogenous blastemas of black axolotls, and vice versa. 

 Although these tissues differed in their race differentials, they could be mixed 

 in various ways without any resulting incompatibilities. 



As to the manner in which unfavorable heterodifferentials may in the course 

 of time injure the transplant, older observations of Braus gave no indica- 

 tions of differences between the results of auto- and homoiotransplantations 

 of buds of extremities in anuran larvae; the transplants survived even 

 through the period of metamorphosis, and extremities of host and donor 

 metamorphosed at the same time. But, transplantations of buds of Bombinator 

 larvae to larvae of Rana esculenta were only temporarily successful. The 

 transplants began to develop and then, when a certain stage had been reached, 

 growth and development ceased. Growth seems, thus, to be a more delicate 

 indicator of incompatibility of organismal differentials than the life of the 

 transplant; the former may stop under the influence of injurious factors 

 of a heterogenous nature at a time when life still continues. As to the cause 

 of cessation of growth at a certain stage, Braus believes that the critical time 

 coincides with the period when the circulation is established in the host. This 

 would suggest that heterotoxins are carried from the host to the transplant 



