32 INTRODUCTION. 



distinguished. CuviER and LAMARCK at first divided animals 

 into two large primary classes : those which have an internal 

 skeleton, and those without a skeleton. They called the first, in 

 as much as the principal part of the skeleton is the vertebral 

 column (see above, p. 24), Vertebrate animals, the last Invertebrate 

 animals (Animaux vertebres et animaux sans vertebres}. Vertebrates 

 have moreover red blood, whilst the division of Invertebrates have 

 either no blood or blood that is white. This fact was known to ARIS- 

 TOTLE, who ascribed a spine to all animals that have blood 1 . Having 

 made these great divisions, they adopted four classes of vertebrate 

 animals, the same as those already established by LINNAEUS, except 

 that they called his amphibia Eeptiles, or creeping animals, a worse 

 appellation. But the number of classes of invertebrate animals has 

 so greatly increased that instead of the two classes, Insects and 

 Worms, first five 2 , and afterwards by LAMARCK 3 , twelve classes, 

 were adopted. 



It would carry us too far away to discuss particularly all these 

 divisions, and the modifications which were introduced into them. 

 It is sufficient for our purpose to remark, that attention was now 

 no longer directed to one organ, or one system of organs, but 

 to the whole organisation. We propose to follow in our work 

 CUVIER'S last arrangement with some modifications, but in a 

 reversed order : whilst he descends from man to the less perfect 

 animals, we, after the example of LAMARCK and others, will begin 

 with the least perfect animals, and ascending gradually to the 

 more composite, will conclude with man. This course is the 

 most advantageous for Physiology. If we would understand the 

 physiological value of an organ, we must investigate its gradual 

 development. 



CUVIER, in his latest works, has followed a general division of 

 the animal kingdom, which takes the place of the two great 

 primary classes of Vertebrate and Invertebrate animals 4 . He per- 



TCL fa, &<ra frai/ut,a tvTiv, 2%ei pa%ij/ 17 dcTrudy, 17 aKavBudrj. Hist. Anim. 

 Lib. in. cap. 7. 



2 See G. CUVIER, Tableau elementaire de VHistoire naturette des Animaux. 8vo. 

 Paris, an. 6 (1793). 



3 DE LAMARCK, Hist. Nat. des Animaux sans vertebres. 8vo. vn. Tom. Paris, 1815 

 1822. 



4 Sur tw nouveau rapprochmcnt a gtablir ks classes qui composent le Regne animal ; 



