Chapter 4. 



The Significance of Organismal Differentials in 



the Transplantation of Pieces of Embryonal 



Tissue into Embryos and into Adult 



Organisms 



In the preceding chapter we have discussed transplantation of parts of 

 organisms, each of which had the ability to live and develop inde- 

 pendently, in invertebrate and amphibian embryos. We shall now con- 

 sider experiments in which smaller pieces of tissue, which under ordinary 

 conditions are not able to live separately or to develop, were grafted into 

 embryos or into adult individuals. Transplantations of this kind in amphibia 

 have been used, especially by Spemann and his associates, in the study of the 

 effects of organizers and their role in embryonal development. This motive 

 rather than the intention of analyzing organismal differentials dominated a 

 large series of such experiments. We shall analyze first, transplantations which 

 were undertaken previous to the full development of the organizer concept, 

 and then in a subsequent chapter we shall discuss transplantations which 

 were carried out with the problem of organizers in view, as far as such 

 experiments are of interest in the analysis of individuality. 



The experiments of Lewis, Filatov and others, have shown that homoio- 

 as well as heterotransplantation of skin can be readily carried out in amphibian 

 larvae, and that in contact with the optic disc the transplant in either case is 

 able to produce the lens of the eye. But the conditions under which the 

 formation of the lens takes place vary in different species. In some species, 

 such as Rana fusca, the skin from all regions of the organism retains up to a 

 relatively late stage of development the ability to produce the lens in contact 

 with the optic vesicle. In Rana esculenta, on the other hand, only the skin 

 of the eye region is able to form the lens, though the transformation of the 

 epithelium of the skin into lens apparently proceeds, through self-differentia- 

 tion, independently of a previous contact with the optic disc. Skin from other 

 areas is not able to produce lens in this species, but the optic disc has the 

 same power to act as an organizer in contact with epidermis as that of other 

 species. Bombinator behaves in a somewhat intermediate manner; certain 

 areas of skin are able to produce lens tissue without contact with the eye 

 vesicle, but the optic vesicle also has the power to induce lens formation in 

 skin with which it is in contact. We have to deal in these cases probably with 

 differences of a quantitative kind, and they seem to depend upon the stage 

 of differentiation which the skin of the various species has attained at certain 

 periods. In principle, there exists in all these species the potentiality of inde- 



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