50 NATURAL HISTORY. 



and not merely some single peculiarity. A ' natural ' 

 classification, therefore, resembles a subject index to a 

 book, rather than a mere alphabetical index. Of course, 

 no perfect classification would be possible unless our 

 knowledge of all animals were perfect ; and as this is not 

 the case, even the best of modern classifications is 

 necessarily, to a larger or smaller extent, an ' artificial ' one. 

 Still, naturalists recognise now, that the merit of a classi- 

 fication is in direct proportion to the extent to which it 

 ceases to be a mere arbitrary or convenient grouping, and 

 is based upon the points of structural or morphological 

 agreement between animals, quite irrespective of such 

 secondary matters as the way in which they live. 



At the period at which Ray lived, our knowledge of 

 animals was not sufficiently extensive to render the framing 

 of anything but an artificial classification possible. More- 

 over, there existed at that time no clear and definite system 

 of zoological nomenclature. What was at that time 

 understood as a ' genus ' was generally what we should 

 now call a 'family/ or, in many cases, even an 'order' 

 of animals. There was also no fixed method of naming 

 ' species ' of animals, so as to clearly indicate by their 

 names what precise place they occupied in their own 

 group. As ah example of this, we may take the British 

 species of the Crow family, and contrast their names at 

 the present day with those employed by Ray : 



Ray's nomenclature. Modern nomenclature. 



1 . Raven Corvus Corvus cor ax. 



2. Carrion-crow Comix Corvus corone. 



3. Rook Comix frugilega Corvus frugilega. 



4. Hooded-cro w Comix cinerea frugilega . . . Corvus comix. 



5. Jackdaw Monedula Corvus monedula. 



6. Chough Coracias Fregilus graculus. 



