GREGARINIDA, RHIZOPODA, SPONGIDA, AND INFUSORIA. 5 



physiological science, in its present state, furnishes us with any 

 means of reasoning from the one to the other. 



Cuvier, the more servile of whose imitators are fond of citing 

 his mistaken doctrines as to the nature of the methods of palaeon- 

 tology against the conclusions of logic and of common sense, has 

 put this so strongly that I cannot refrain from quoting his words.* 



" But I doubt if any one would have divined, if untaught by 

 observation, that all ruminants have the foot cleft, and that they 

 alone have it. I doubt if any one would have divined that there 

 are frontal horns only in this class : that those among them 

 which have sharp canines for the most part lack horns. 



" However, since these relations are constant, they must have 

 some sufficient cause ; but since we are ignorant of it, we must 

 make good the defect of the theory by means of observation • 

 it enables us to establish empirical laws, which become almost 

 as certain as rational laws when they rest on sufficiently re- 

 peated observations ; so that now, whoso sees merely the print of 

 a cleft foot may conclude that the animal which left this im- 

 pression ruminated, and this conclusion is as certain as any 

 other in physics or morals. This footprint alone, then, yields to 

 him who observes it, the form of the teeth, the form of the jaws, 

 the form of the vertebras, the form of all the bones of the legs, of 

 the thighs, of the shoulders, and of the pelvis of the animal which 

 has passed by : it is a surer mark than all those of Zadig." 



Morphological classification, then, acquires its highest im- 

 portance as a statement of the empirical laws of the correlation of 

 structures ; and its value is in proportion to the precision and 

 the comprehensiveness with which those laws, the definitions of 

 the groups adopted in the classification, are stated. So that, 

 in attempting to arrive at clear notions concerning classification, 

 the first point is to ascertain whether any, and if so, what groups 

 of animals can be established, the members of which shall be at 

 once united together and separated from those of all other 

 groups, by well-defined structural characters. And it will be 

 most convenient to commence the inquiry with groups of that 

 order which are commonly called Classes, and which are enume- 

 * ' Oftscmens fossilcs," ed. -i me , tome \ r , p. 164. 



