270 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



specific effects of the organismal differentials of the recipient tissue, were 

 reported by Schotte. He transplanted presumptive skin from the abdomen of 

 anuran Rana or Bombinator gastrula into the mouth region of urodele Triton 

 or Amblystoma embryos. In the transplants there developed mouth organs 

 under the influence of the organizers of Triton and Amblystoma; however, 

 whereas in the latter species a balancer would have formed, in the anuran 

 transplants anuran mouth organs, such as suckers, horny jaws and teeth, as 

 well as operculum, developed, each one in its characteristic place. We must 

 therefore conclude that the organizers in the mouth organs of Triton or 

 Amblystoma tend to induce amphibian mouth organs in general, but not the 

 specific urodele mouth organs. The character of the recipient tissues, and in 

 particular the characteristics determined by the organismal differentials or 

 their precursors inherent in the transplant, determine what species charac- 

 teristics these organs shall possess. It is, of course, possible, although not very 

 probable, that in addition to the organizer substances, other less specific factors 

 localized and inherent in the mouth region, participate in bringing about this 



result. 



These findings again show the intimate connection which exists between 

 the organizers, whose functioning leads to the development of specific tissues 

 and organs, and the organismal differentials. A similar connection was noted 

 in the case of inductions produced in the transplant by the host tissues, or in 

 the host tissues by the transplant, in phylogenetically primitive classes of 

 animals. Here, also, we observed that the species characteristics of the strange 

 tissues were fixed, but that the determination of the kind of organ which was 

 to develop was influenced by the inducting substances which asserted them- 

 selves, notwithstanding the strangeness of the organismal differentials. 



While we have so far reviewed only experiments in amphibia, in principle, 

 similar conclusions hold good also in other classes of animals. Thus in the 

 chick embryo at the stage of the primitive streak formation, the potentiality 

 of embryonal parts to form various tissues and organs is greater than is 

 indicated by the tissues and organs which actually are produced during normal 

 embryonal development. This fact has been established by means of trans- 

 plantation of parts of the embryo into the chorio-allantois of the chick embryo. 

 In this way it has been found, for instance, that heart can be produced at three 

 different levels, and gut may develop from all levels of the primitive streak. 

 The portion anterior to the pit can produce liver and mesonephros and the 

 portion posterior to the pit can produce adrenal (Hunt). In the normal 

 embryo substances are presumably given off by tissues, which inhibit the 

 development of certain neighboring tissues and organs in a similar manner to 

 that noted in the two-cell stage of echinoderm eggs, when one blastomere 

 inhibits the other from developing into a whole embryo. But other tissues which 

 normally develop in the embryo in a certain place, may not develop if isolated 

 parts of the embryos are transplanted, perhaps because under the conditions 

 of isolation needed organizer substances may be lacking. Furthermore, we may 

 assume that the ability of the embryo to form tissues varies in the direction 

 from the oral to the aboral pole of the primitive streak and also in a lateral 



