14G niSTORY OF THE WORKS OF CUVIER. 



tion and resDimtion, which come immediately after the nei-vons system in the 

 order of their importance, will give the tirst subdivisions, or the classes. The 

 vertehraie animals present either a simple and complete respiration, with a dou- 

 ble circulation, which is the case with the mammifers; or a double respiration 

 and double circulation, which is the case with birds; or a simple respiration, but 

 complete one, since it is alwa3^s aerial, and this combined with a simple circula- 

 tion, being the case of reptiles; or a double circulation, combined with an incom- 

 plete, thai'', is to say an aquatic, respiration, which is the case ^\\\\\ fishes. Hence 

 the vertebrate animals are distributed, according to their organs of circulation 

 and respiration combined, into four classes — the mammifers, birds, reptiles, and 

 fishes. 



So it is, also, with the mollusJcs; some have three hearts, others two, others 

 one : of these hearts there are such as have but a single ventricle and a single 

 anricle ; others a single ventricle and two auricles ; others, again, a single ven- 

 tricle without an auricle,, &c. ; in fine, certain mollusks respire by a pulmonary 

 cavity, others by branchia;, &:c.; and it will be readily conceived that the com- 

 bination of all these variations of respiratory and circulatory organs will furnish 

 classes of mollusks as it furnished the classes of vertebrata. The classes of 

 mollusks, thus determined, are six in number — ceplialopods,gasteyopods, acejjJuilatcs, 

 liieropods, hracliiopods, and cirrhojwds. 



Tiie combination of the organs under consideration will give us, likewise, and 

 in even a still more striking manner, the subdivision of the third branch 

 into four classes: the annelids, whose blood is red like that of the vertebrata; 

 the Crustacea, whose blood is white like that of all other animals without verte- 

 brae, and which, moreover, have a heart placed in the back, &c. ; the arachnids, 

 which have for heart only a simple dorsal vessel which sends forth arterial branches 

 and receives venous ones; and insects, v:\nch have no vessels at all, neither 

 arteries nor veins, which have only the vestige of a heart, and whose respiration 

 is not effected by circmnscribed organs, but b}'' trachece, or elastic vessels distrib 

 uted through the whole body. In this branch of the articidata we observe, 

 therefore, the transitimi from animals which have a circulation to those which 

 have none, and the corresponding transition from those which respire by means 

 of circumscribed branchite to those in which trachea distribute the air to every 

 part. 



It is in the fourth branch, or that of zoophytes, or the radiata, that we 

 observe the disappearance, the gradual and successive fusion of all the organs 

 into the general mass. Thus, some of these animals have still closed vessels, 

 distinct organs of respiration, &c. ; others, which have neither such vessels, for 

 circulation nor such organs for respiration, have still visible intestines; it is only 

 in the last of all that everything seems reduced to a homogeneous pulp ; and it 

 is on the different degrees of complication in their structure that is founded their 

 subdivision into five classes: cchinoderms, intestinal worms, acalephs, polyps, 

 and infusoria. ******* 



Thus the nervous s^-stcm has furnished the branches; the organs of circu- 

 lation and respira,tion combined, the c/«6'5e5; audit is cas}'- to conceive that organs 

 more and more subordinate would successively supply the orders, the families, 

 the tribes, the genera, the sub-genera, in a word, the whole scaffolding of the 

 method. Thus as regards the mammals, for instance, (for it would detain us too 

 long to follow the unfolding of the method in all the classes,) the combined 

 organs of touch and oi inanducation divide this class into nine orders: man, who 

 has three sorts of teeth, (molar, canine, and incisive,) and who has the opposable 

 thumb on the two anterior extremities alone ; the quadrumana, which have also 

 the three sorts of teeth, and, moreover, the opposable thumb on the four extrem- 

 ities ; the carnivora, wliich again have the three sorts of teeth, but no opposable 

 thumb and consequently no hands, which have only feet, bat feet of which the 

 digits or toes are movable, like those of the two above orders; the rodents, whose 



