ON THE VITALISTIC VIEW OP NATURE. 449 



supposes the fact of heredity that is, the transmission 

 of characters peculiar to the parents (be they acquired 

 by them or not), and the fact of variation, but it does 

 not explain them. It does not give any intelligible 

 description of the means which nature uses to secure 

 that continuity of change which is marked on the one 

 side by a faithfulness to certain typical forms, and on 

 the other by a gradual development. The cellular 

 theory permits us to comprise, under the general 

 categories of cell-growth, cell-division, and cell-fusion, 

 the great facts of the history of all living matter, but 

 it does not explain how that apparent sameness of 

 structure which the ultimate morphological unit, the 

 cell, presents to our view, develops into that variety 

 of recurrent forms which make up the wealth and 

 the order in the world of natural objects. The older 

 naturalists were divided into two distinct schools : one 

 believed in pre-formation with development the older 

 meaning of " evolution " ; the other in after-formation, 

 or " epigenesis." The former foundered on the difficulty 

 of explaining or making plausible how all the germs 

 of hundreds of succeeding generations could be contained 

 in the first ancestor; the latter failed to explain how 

 nature was able to build up by mechanical forces out 

 of unorganised matter a structure resembling the parent 

 structures. The suggestion of a " nisus formativus," 

 which we owe to the celebrated Blumenbach, is only 

 a definition of the difficulty, not an explanation. 



The three distinct ideas represented by these historic 

 terms occur again in modern biology, though altered to 

 suit the vast extension of actual knowledge of facts, and 



VOL. II. 2 F 



