XL] EVOLUTION IN BIOLOGY. 299 



organisation which is presented by living beings, and 

 culminated in the doctrine of the " echelle des etres," 

 so powerfully and clearly stated by Bonnet; and, 

 before him, adumbrated by Locke and by Leibnitz. 

 In the then state of knowledge, it appeared that all 

 the species of animals and plants could be arranged in 

 one series; in such a manner that, by insensible 

 gradations, the mineral passed into the plant, the 

 plant into the polype, the polype into the worm, and 

 so, through gradually higher forms of life, to man, at 

 the summit of the animated world. 



But, as knowledge advanced, this conception ceased 

 to be tenable in the crude form in which it was first 

 put forward. Taking into account existing animals 

 and plants alone, it became obvious that they fell into 

 groups which were more or less sharply separated from 

 one another ; and, moreover, that even the species of 

 a genus can hardly ever be arranged in linear series. 

 Their natural resemblances and differences are only 

 to be expressed by disposing them as if they were 

 branches springing from a common hypothetical 

 centre. 



Lamarck, while affirming the verbal proposition 

 that animals form a single series, was forced by his 

 vast acquaintance with the details of zoology to limit 

 the assertion to such a series as may be formed out of 

 the abstractions constituted by the common characters 

 of each group. 1 



1 " II s'agit done de prouver que la serie qui constitute 1'echelle 

 animale reside essentiellement dans la distribution des masses princi- 

 pales qui la composent et non dans celle des especes ni meme tou- 

 jours dans celle des genres." " Phil. Zoologique," chap. v. 



