1 86 THEORETICAL BIOLOGY 



account by the constructor when he is making the implement. 

 On the completed article, they separate both the " functional " 

 and the " genetical " building-stones from one another. 

 When they occur, the division lines between morphological 

 and physiological organs coincide. 



Let us consider an implement composed entirely of very 

 small and similar building-stones — a brick staircase, for 

 example — and let us inquire whether it could not have come 

 into existence of itself, through mere use, or whether any con- 

 structional process is demonstrable which is independent 

 thereof. We are obliged to look for such signs as are not of 

 a functional but of a genetic kind, i.e. for pure signs of genesis, 

 not coincident with the signs of function. 



The joins are not necessarily the only pure signs of genesis. 

 On the contrary, every indispensable property of the imple- 

 ment that bears no relation to the functions, may be so classi- 

 fied. Think, for instance, of the rough rim on the under side 

 of every china plate, which is elsewhere covered all over with 

 smooth glaze. Here we are confronted with a pure sign of 

 genesis, reminding us that, when it was being fired, the plate 

 stood on a red-hot support, which prevented the glaze from 

 forming there. 



On the other hand, when we examine a willow wand that 

 is used as a bow, and find that the woody fibres on the one 

 side are permanently more stretched than those on the other, 

 we shall explain this as a sign of function, referable to use 

 alone. 



Even if all our implements were composed of a three- 

 dimensional mosaic of very minute elements, we might neglect 

 this investigation into signs of genesis and of function, for the 

 history of the genesis of these things of our own manufacture 

 rests with ourselves. We should know precisely which altera- 

 tions of the elementary mosaic had been effected by con- 

 struction, and which by function. 



