xxn.] CLASSIFICATION. -28S 



Thus the branches of our symbolical organic tree should 

 never reunite after dividing, and should generally ascend. 

 Do the facts support these a priori conclusions ? 



So far as the facts are known they do. It is a familiar Groups 

 remark to naturalists that groups are united by their lower ^e^gjallv 

 rather than by their higher members. Were this univer- united by 

 sally true, it is obvious that the organic tree would have members. 

 its branches always ascending and never reuniting. This 

 is a subject of great importance, and I must illustrate it 

 further. The organic tree consists of two main trunks, 

 the vegetable and the animal. It is by the lowest mem- 

 bers of both groups that they are brought into contact. 

 There are many forms concerning which it is uncertain 

 whether they are animal or vegetable ; and perhaps, in- Animal 

 deed, we make ourselves the slaves of our own words vegetable 

 when we assume that every organism must be definitely kingdoms. 

 either the one or the other. The sarcode of which the 

 bodies of the Protozoa are composed does not appear 

 essentially to differ from the protoplasm contained in 

 vegetable cells ; and if it is true, as I think most pro- 

 bable, that this community of properties indicates com- 

 munity of origin, the germ, or germs, from which both Their 

 the vegetable and animal kingdoms have been descended, commoix 

 must have been neither decidedly vegetable nor de- origin- 

 cidedly animal, but capable of acquiring the properties 

 of either. 



This is perhaps the best of all the many instances which 

 might be enumerated of the general law that groups are 

 united by their lowest members, and separated in their 

 higher forms. We have seen that it is nearly impossible No abso- 

 — I am inclined to think quite impossible— to make anv ^'^^^ .• 



. . ^ ^ •' distinetioa 



absolute distinction between the lowest plants and the between 

 lowest animals. But between their highest forms the ^^^'^^ 

 distinction is not only fundamental, but is also so obvious 

 that it cannot be mistaken. The warm-blooded Verte- Their 

 brata are the highest of all animals ; and, though there ^^^^^^"^ . 

 is no vegetable class that stands so decidedly at the head totally 

 of that kingdom, we cannot be far wrong if we regard 

 the Eosacese and their allies as the most highly organized 



