236 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



circulation at all and death followed. Also in the subsequent experiments of 

 Braus, who showed that under favorable conditions the life of such combina- 

 tions could be prolonged for as long as five weeks, ultimately serious incom- 

 patibilities developed. However, union between members of different orders 

 (urodeles and anurans) did not succeed for longer than one or two days. 



When thus heterotransplantations between nearly related species succeed 

 well, this does not necessarily mean that heterodifferentials do not exist in 

 their tissues, but merely that the intensity of the reaction against the strange 

 organismal differentials does not preclude a successful transplantation. How- 

 ever, if the conditions under which such heterotransplantations take place 

 are less favorable, then the existence of incompatibilities between the heterog- 

 enous organisms may become manifest. Hence, while the parabiosis-like 

 union between different species of Rana could be readily accomplished, ex- 

 change of pieces of skin between the larvae of different species of Rana did 

 not succeed; within a few days the grafts became smaller and then disap- 

 peared. As for the raising of such combinations of embryos to a stage further 

 than metamorphosis, Born succeeded only in the case of homoiogenous graft- 

 ing of embryos of Rana esculenta. He did not succeed in reaching this stage 

 with heterogenous combinations, although in other respects, as noted above, 

 heterotransplantations between nearly related species behaved about like 

 homoiotransplantations. 



The experiments of Born were continued by Harrison, who in one instance 

 kept alive a heterogenous combination (Rana virescens and Rana palustris) 

 through the period of metamorphosis and was able to observe that each of the 

 two constituents in this combination retained its characteristic species features. 

 But the size of a whole animal of this kind was much smaller than that of a 

 normal frog. In general, such heterogenous combinations, although able to 

 eat and shift for themselves, became weak in the course of time, they de- 

 creased considerably in size and finally died ; at most, they could be kept alive 

 for three or four months, while in Born's experiments similar heterotrans- 

 plantations succeeded only for a period of three weeks. But even in Harrison's 

 experiments atrophy and degeneration in the large majority of cases set in 

 after a few weeks. This investigator also observed that if a tail had been 

 grafted to an individual of a different species, there was noticeable an early 

 interference not only with the growth, but also with the life of the grafted 

 tail, parts of which, however, could remain viable for a longer time. 



Harrison furthermore noted that in some instances reciprocal transplanta- 

 tions behaved in an unlike manner, an effect which has been found also in 

 other kinds of transplantations and to which we have previously referred. Of 

 interest also is his observation that the lateral organs of one partner could 

 grow into the other, although the partners belonged to different species, as 

 happened when the tail portion of Rana palustris was joined to the anterior 

 part of Rana sylvatica; in this case the lateral line organs extended from 

 Rana palustris into Rana sylvatica. Evidently there was here no very marked 

 incompatibility between parts of organs possessing, each one, its own species 

 differential ; if antagonistic reactions did occur under these conditions, they 



