144 EVOLUTIONISTS OF THE EIGHTEENTH CENTURY. 



embryo. In the original formation of the embryo 

 he rejects the Pangenesis theory of Buffon, that is, 

 of the conjugation of Hke parts from the two par- 

 ents. " These organic particles, he (Mr. Buffon) 

 supposes to exist in the spermatic fluids of both 

 sexes, and that they are derived thither from every 

 part of the body, and must therefore resemble, as he 

 supposes, the parts from whence they are derived." 

 He substitutes for this a theory of his own, of the 

 addition of parts, which takes little account of the 

 laws of heredity. 



The individual life begins, as all life originally be- 

 gan, from a single filament. " Shall we conjecture," 

 he says, "that one and the same kind of living fila- 

 ment is and has been the cause of all orofanic life t 

 . . . I suppose this living filament, of whatever 

 form it may be, whether sphere, cube, or cylinder, to 

 be endowed with the capability of being excited into 

 action by certain kinds of stimulus." This irrita- 

 bility and excitability is the first step in Darwin's 

 conception of Evolution. • It is that whereby ani- 

 mals and plants react to their environment, causingi 

 changes in their own structure, and these changes 

 are transmitted to their offspring. 



In this chapter upon Generation, he throws out 

 a wealth of suggestion and inquiry which indicates 

 a thorough appreciation of the problems which 

 were yet to be solved, as well as of the broadest 

 aspects of Evolution. He touches upon Embry- 

 ology, Comparative Anatomy, the Colouring of 



