oe INTRODUCTION. 
distinguished. Cuvinr 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 vertébrés et animaux sans vertébres). 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?!. Having 
made these great divisions, they adopted four classes of vertebrate 
animals, the same as those already established by Linn aus, except 
that they called his amphibia Reptiles, 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?, and afterwards by LAMARCK®, 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. 
CuvieER, 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*. He per- 
1 Tldvra ra (Ga, boa Gaya éorw, exer paxw 7H doTGdn, 7 axav0Gdyn. Hist. Anim. 
Lib. 101. cap. 7. 
2 See G. Cuvier, ZVableau élémentaire de 0 Histoire naturelle des Animaux. 8yo. 
Paris, an. 6 (1793). 
3 Dr Lamarox, Hist. Nat. des Animaua sans vertébres. 8vo. vit. Tom, Paris, 1815 
—1822. 
4 Sur un nouveau rapprochment a établir les classes qui composent le Regne animal ; 
