IN NATURAL HISTORY. 9 



fonde'es sur le deVeloppement ou l'addition de 

 quelques parties, qui ne changent rien a l'essence 

 du plan."* 



Tlie value of this principle was soon tested by 

 its application to facts already known, and it was 

 found that animals whose affinities had been 

 questionable before were now at once referred 

 to their true relations with other animals by as- 

 certaining whether they were built on one or 

 another of these plans. Of such plans or struc- 

 tural conceptions Cuvier found in the whole ani- 

 mal kingdom only four, which he called Verte- 

 brates, Mollusks, Articulates, and Radiates. 



With this new principle as the basis of investi- 

 gation, it was no longer enough for the naturalist 

 to know a certain amount of features character- 

 istic of a certain number of animals, — he must 

 penetrate deep enough into their organization to 



* If we consider the animal kingdom according to the princi- 

 ples advanced above, — freeing ourselves at the same time from 

 prejudices founded on previously established divisions, and look- 

 ing at animals only with reference to their nature and or- 

 ganization, excluding their size, their utility, our greater or less 

 familiarity with them, and all other accessory circumstances, — 

 we shall find that there exist four principal forms, four general 

 plans, if we may so express it, in accordance with which all 

 animals seem to have been modelled, and the ulterior divisions 

 of which, by whatever title naturalists may have dignified them. 

 »re only comparatively light modifications, fonnded on the de 

 velopment or the addition of some parts not affecting the essea 

 tial elements of the plan, 

 i* 



