I I 2 THE GERM-PLASM 



determinants for the testes and ovaries. The suppicmetitary 

 deteynii)ia}its with which the idioplasm of certain cells of the 

 vertebral colunui was provided for the purposes of regeneration^ 

 must have become changed in the course of phytogeny. 



A transmissible variation of this kind must, however, also have 

 had some effect on embryogeny, if only one and the same deter- 

 minant were present in the germ-plasm for the two modes of 

 development. Hence each determinant of these caudal vertebrce 

 must be doubled in the germ-plasm. 



It would be premature to go beyond this assumption, and to 

 attempt to decide anything about the manner in which the 

 various supplementary determinants which are required for the 

 restoration of one of the larger parts — such as, for instance, 

 the caudal vertebrae — come together, and how and when they be- 

 come separated from the primary determinants. The processes 

 of regeneration have not as yet been examined from the point of 

 view which I have here suggested ; and in many cases it is not 

 even known for certain from what cells regeneration proceeds. 



Hitherto we have not discussed in detail the question as to 

 the kind of cells which contain the supplementary determinants^ 

 and from which regeneration thus takes place. May these 

 determinants be present in any kind of cell belonging to any 

 tissue, or is their distribution always limited to young and 

 apparently undifferentiated cells of the so-called ' embryonic 

 type ' ? 



If w'e only consider Man and the higher Vertebrates, we shall 

 be disposed to look upon the latter of these two alternatives as 

 the one which is in general correct. Even recently, in fact, 

 many authors seemed to be in favour of this view : ' embryonic 

 cells ^ were supposed to be contained in all those tissues which 

 are capable of regeneration, and it was, indeed, believed by 

 many that the leucocytes are cells of this nature. The latest 

 investigations, however, lead us to the conclusion that this is 

 not the case, and that although the white blood corpuscles are 

 extremely important as conveyers of nutriment in the process of 

 regeneration, they do not serve as formative elements in the 

 construction of a tissue. In his text-book on Pathological 

 Anatomy, Ziegler speaks of a formal ' law of the specific 

 character of the tissues,' w^hich he explains as follows : — ' the 

 successors of the various germinal layers which separate from 

 one another at an earlv embrvonic stas^e, can onlv give rise to 



