456 PROCEEDINGS OF THE ACADEMY OF [Juljr 



and air, and, on the other, to the physical factors, light and tem- 

 perature, variations are bound to occur. If, however, these varia- 

 tions are constant for a series of successive generations and can be 

 demonstrated in cell-contents, cell-walls and cell-functions, then a 

 species has been formed, but not otherwise. 



In the inorganic world, as we well know, physical and chemical 

 tests both are oftentimes necessary to prove the identity or specific 

 nature of a substance. Likewise in the biological world physical 

 and chemical tests of cell-contents, cell- walls and the products of 

 cell-function are necessary to establish the specific character of an 

 individual. 



The author desires to acknowledge his indebtedness to Florence 

 Yaple, of Philadelphia, for valuable assistance in the preparation* 

 of this paper. 



