308 EVOLUTION IN BIOLOGY. 



mental characters, by which any one of Cuvier's great 

 groups shall be separated from all the rest. On the con- 

 trary, the lower members of each tend to converge 

 towards the lower members of all the others. The same 

 may be said of the vegetable world. The apparently 

 clear distinction between flowering and flowerless plants 

 has been broken down by the series of gradations 

 between the two exhibited by the Lycopodiacece, RKizo- 

 carpece, and Gymnospermece. The groups of fungi, 

 Lichenes, and Algce have completely run into one another, 

 and, when the lowest forms of each are alone considered, 

 even the animal and vegetable kingdoms cease to have a 

 definite frontier. 



If it is permissible to speak of the relations of living 

 forms to one another metaphorically, the similitude 

 chosen must undoubtedly be that of a common root, 

 whence two main trunks, one representing the vegetable 

 and one the animal world, spring; and, each dividing 

 into a few main branches, these subdivide into multitudes 

 of branchlets and these into smaller groups of twigs. 



As Lamarck has well said * 



" II n'y a que ceux qui se sont longtemps et forteraent occnpes 

 de la determination des especes, et qui ont consulte de riches col- 

 lections, qui peuvent savoir jusqu'a quel point les especes, parmi les 

 corps vivants se fondent les unes dans les autres, et qui ont pu se 

 convaincre que, dans les parties ou nous voyons des especes isoles, 

 cela n'est ainsi que parcequ'il nous en manque d'autres qui en sont 

 plus voisines et que nous n'avons pas encore recueillies. 



" Je ne veux pas dire pour cela que les animaux qui existent 



* Philosophic Zoologique, premi&re partie, chap. iii. 



