BONNET'S THEORY OF EVOLUTION. 



22 9 



That part of the old epigenesis which started the germ as "a 

 sort of living precipitate " in a clear fluid (" colliquamentum "), 

 is of course set aside, and along with it the absurdities of Bon- 

 net's idea of metamorphosis (change of external form without 

 change of structure or substance). 



In place of these errors are put the ready-made germ, with 

 a structure received from the parent organism, impregnation 

 by fusion of two germs, and development by a process of divi- 

 sion. Evolution is viewed as " a course of progressive differ- 

 entiation " " a succession of changes of the form, structure 

 and functions of the germ by which it passes, step by step, 

 from an extreme simplicity, or relative homogeneity of visible 

 structure, to a greater or less degree of complexity or hetero- 

 geneity." (Ibid., p. 199.) 



" From this point of view," says Huxley, "the process 

 which in its superficial aspect is epigenesis, appears in essence 

 to be evolution in the modified sense adopted in Bonnet's later 

 writings ; and development is merely the expansion of a poten- 

 tial organism, or 'original preformation,' according to fixed 

 laws." (Ibid., p. 204.) 



The position here so concisely sketched in 1878, is the one 

 toward which opinion seems to be drifting. But while the 

 philosophy is clear, the identification of it, or any part of 

 it, with Bonnet's later views is, I believe, unwarranted by 

 anything contained in Bonnet's writings. The comparison, 

 if it be inadmissible, is all the more unfortunate for the sanc- 

 tion of an authority so universally respected. It has been 

 taken for considerable more than its author would probably 

 approve ; for some have construed it against epigenesis, and 

 others against evolution. 



We should have no fault to find with the comparison if it 

 were true, as Huxley seems to have supposed, that Bonnet 

 finally adopted a definition of the germ which dropped the 

 chief distinction between evolution and epigenesis, as under- 

 stood in his time. I do not find any such inconsistency be- 

 tween Bonnet's earlier and later definitions, and it is very 

 certain that Bonnet never made any concession which, to his 

 understanding, weakened in the least degree his idea of pre- 



