394 WILLIAM H. COLE 



differences between different regions of an animal's body in their 

 chemical and physiological reactions. For example, when the 

 anterior and posterior ends are differentiated, the animal is said 

 to show 'polarity' or to possess 'axial gradients.' Such terms may 

 be used merely to describe conditions, but when they are employed 

 to express the cause of regional differences, the solution of the 

 problem is only delayed. However, if specific chemical differ- 

 ences in the cells of the regions concerned can be demonstrated, 

 then the explanation of differences in form, structure, and func- 

 tion will be easier. 



In the frog tadpole it has here been shown that integument in 

 the tail region is specific and retains its individuality even when 

 transferred to a new soil. Similarly, skin from the back or the 

 belly transplanted to the tail continues to produce back or belly 

 skin, respectively, and preserves its individuality indefinitely. 

 There must be, therefore, in the integument of these regions 

 different substances which are constantly being produced by the 

 cells and which determine the character of the new cells formed. 



Two observations in which local specificity of skin in different 

 regions of an animal has been noted have come to the attention 

 of the writer. These are both reported by Schone ('12). He 

 describes reciprocal autoplastic grafts of belly and back skin in 

 mice, and states that each kind of skin retains its individual 

 characteristics when transplanted to the other region. He then 

 quotes (p. 97) the experience of Marchand. In examining a 

 graft of arm skin on the nose of a man, presumably autoplastic, 

 Marchand found that all the characteristics of arm skin had been 

 preserved two years after the operation. Including the evidence 

 derived from the experiments reported here, there is ground for 

 saying that in frog tadpoles, mice, and human beings a local 

 specificity of integument exists. 



