LINN/EUS AND THE LINNEAN CLASSIFICATION. 49 



not express the real relationships of the animals grouped 

 together. Hence, this arrangement separates certain 

 animals which are closely allied to one another, and places 

 others in juxtaposition between which there is no real 

 affinity. Thus, the Cetaceans (whales and dolphins) are 

 separated from the ordinary quadrupeds, with which they 

 agree, in all really essential points, simply upon the trivial 

 ground of their aquatic habits; though Ray places the 

 almost equally aquatic Seals in their right place, and even 

 puts the Manatees (sea-cows) among the ordinary Mam- 

 mals. Again, the birds, by the structure of their heart, are 

 placed in the same primary division as the Mammals, 

 whereas their true affinities are with the Reptiles, in spite 

 of the incomplete heart possessed by the latter. 



The above classification, therefore, does not express 

 the true order of nature, or indicate correctly the real 

 relationships that subsist between different groups of 

 animals. Like all 'artificial' classifications, it is essenti- 

 ally a mere index to the book of nature; and though 

 extremely useful for the purpose of discriminating between 

 different species of animals, it no more expresses the 

 relationships of these species to each other, than a good 

 index would enable one to recognise the connection, 

 between the different subjects of a volume. 



On the other hand, a classification is a ' natural ' one 

 just so far as it does express these relationships. On a 

 really ' natural ' classification, animals are grouped together 

 according to their true affinities to each other; and as 

 these affinities are manifested in all the parts of the 

 organisation of animals, so the characters which are used 

 in such a classification are those of the entire structure, 



