80 
SYSTEM OF NATURE. 
it are observable in some, while in others its functions ap¬ 
pear to be performed by an indurated skin, which serves 
for the attachment of the muscles. The circulation is 
equally imperfect, never (I should suppose) altogether ab¬ 
sent, but often unconfined by the vessels which invariably 
limit its course in the vertebrated groups. Respiration un¬ 
dergoes a like modification; instead of being confined to the 
lungs it is ramified more or less through the entire body. 
Cuvier tells us that before his time modern naturalists 
divided all invertebrate animals into two classes,—insects 
and worms, — a method which he was the first to attack ; 
and in a paper read before the Society of Natural History 
of Paris, on the 10th of May, 1795, and printed in the 
4 Decade Philo soph ique,’ he presented a new division, in 
which he defined the characters and limits of Crustacea, 
Insects, Echinodermata, Zoophytes, Mollusca and Worms. 
Subsequently, however, he distributed the animal king¬ 
dom into four great divisions, under the names of Verte- 
brata, Mollusca, Articulata and Radiata. These divisions 
partially correspond with those previously proposed, the 
Articulata comprising three of the earlier groups,—name¬ 
ly, Worms, Crustacea and Insects, — and the Radiata two, 
Echinodermes and Zoophytes. In the 4 Regne Animal’ 
the Annelides or red-blooded worms are again cut off from 
the other articulated animals, and placed immediately after 
the Mollusca, so that there is really little discrepancy be¬ 
tween the views entertained by this great zoologist at dif¬ 
ferent periods of his career; his earliest views favoring a 
division into seven single groups, which by degrees ap¬ 
peared to resolve themselves into a single one and three 
pairs. The discrepancy therefore between the views of this 
great man, as expressed at various periods of his bright 
