BARON CUVIER. 41 



jlood is the atmospheric air, it penetrates even into the in- 

 terior of the respiratory organ ; but when it is water, it 

 simply glides over a surface, more or less multiplied. These 

 surfaces, or leaflets, are called branchiae, and are found in 

 fishes, and many of the mollusca. Instead of leaflets, there 

 are sometimes tufts, or fringes. Air penetrates into the 

 body by one or several orifices. In the first instance, which 

 is that of all animals with lungs, properly so called, the chan- 

 nel which receives the air is subdivided into a multitude of 

 branches, which terminate in as many little cells, generally 

 collected into two masses, which the animal has the power 

 of compressing or dilating. When there are several open- 

 ings, wh ich we see only in insects, the vessels which receive the 

 air are ramified to infinity, in order to carry it to every part of 

 the body without exception, and this is what is called respi- 

 ration by means of tracheae. Lastly, the zoophytes, with the 

 exception of echinodermes, have no apparent organ of respi- 

 ration." 



In the third portion of this opening lecture, the affinities 

 of organs are described, and their manner of acting on each 

 other. " Of what use," says M. Cuvier, " would sensation 

 be to us, if muscular force did not help it, even in 

 the most trifling circumstances ? What use could we make 

 of touch, if we could not carry our hands towards the 

 palpable object ? and what should we behold if we could 

 not turn our eyes or head at pleasure? It is on this 

 mutual dependence between the functions, and on this re- 

 ciprocal aid, that the laws are founded which determine the 

 affinities of the organs of animals ; which affinities are as 

 necessary to them, as metaphysical or mathematical laws 

 are to other parts of the creation. For it is evident, that a 

 suitable harmony between those organs which act upon 

 each other, is a necessary condition to the existence of the 

 being to which they belong ; and that if one of these func- 

 tions were modified in a manner incompatible with the mo- 

 difications of others, that being could not exist. Modern 

 experiments have shown, that one of the principal uses of 

 respiration is to re-animate muscular force, by restoring to 

 the muscular fibres their exhausted irritability, and, in fact, 

 among the animals which breathe the air in a direct man- 

 ner, we see those with double circulation, and not an atom 



