12-1 MEMOIR OF CUVIER. 



still more eminent degree of sagacity of obsen^ition transferred to all the partg 

 of the animal — to its muscles, its vessels, its nerves, its organs of sense. Swam- 

 merdam, and Pallas,* who had embraced all the parts of the animal in their anatom- 

 izations, had confined these to certain species ; in another genus Lyonnet had 

 ctmfincd himself to a single one ; in the case of Cuvier there was an entire class 

 of animals, and of all animals the class least known, of whicli almost all the 

 species were described and all the details, even the most delicate and obscure, 

 of their structure were brought to light and developed. 



The moUnsJcs have all a heart, as already said ; some, however, have but a 

 single one, like the oyster and snail; others have two ; others again, lilie the 

 poulp and cuttle-fish, have as many as three distinct hearts. And yet it was 

 with these animals whose organization is so ricli, which have a brain, nerves, 

 organs of sense and of secretion, that it had been the custom to confound others, 

 which, like the zoophytes and polypes, for example, have for their whole organi- 

 zation only an almost homogeneous i)ul}). 



The experiments of Trembley have rendered famous the polypus of fresh 

 water, that animal which puts forth buds like a plant, and each part of which, 

 separated from the others, forms a new and complete individual. The whole 

 structure of this singular zoophyte reduces itself to a sac^ — that is to say, to a 

 mouth and stomach. M. Cuvier has made known another zoophyte,t whose 

 structure presents something still more surprising, for it has not even a mouth; 

 it is nourished by means of ramified suckers, like plants, and its internal cavity 

 serves by turns as a stomach and sort of heart, for vessels enter it which con- 

 duct to it the nutritive juices, and other vessels issue from it which convey these 

 juices to the members. 



One of the most curious pi'oblems of the physiology of white-hlooded anhncils 

 which has been resolved by M. Cuvier is that of tlie nutrition of insects. Insects, 

 as has been already said, liave, in place of a heart, only a simple dorsal vessel; 

 and, moreover, this dorsal vessel has no branch, no ramification, no particular 

 vessel which either enters or issues from it. This was already known through 

 the celebrated researches of Malpighi, Swammerdam, and Lyonnet. But M. 

 Cuvier goes much further; he examines, one after the other, all the parts of the 

 bodies of insects, and by this detailed examination he shows that no sanguineous 

 vessel, or, what amounts to the same thing, no circulation, exists in these ani- 

 mals. How, then, is their nutrition efi'ected? 



M. Cuvier begins by remarking that the final object of the circulation is to 

 conduct the blood to the air. Hence all animals which have a heart have a cir- 

 cumscribed respiratory organ, whether lungs or branchia?, and the blood returned 

 from the members to the heart is invariably constrained to traverse this organ, 

 in order to be there subjected to the action of the air before returning to the 

 members. But in insects the apparatus of respiration is wholly different. It is 

 no longer a circumscribed organ whicli receives the air; it is an immense num- 

 ber of elastic vessels, called trachecc, which convey it into all pans of the body, 

 and which thus conduct it even to the nutritive fluid itself, which continually 

 bathes those parts. In a word, while in other animals it is the nutritive fluid 

 which by means of the circAilation goes in search of the air, the })henomenon is 

 reversed in insects, and it is the air, on the contrary, which goes to seek the 

 nutritive fluid, and thereby renders all circulation useless.| 



Another discovery of M. Cuvier, not less important, is that of the circulatory 

 apparatus of certain worms, such as the earth-worm and leech, whicli had until 

 then been confounded with those ^ooj>h)/tes of a structure incomparably more 



* Poii had -also preceded him in the anatomy of several molluscs, but of mutficalve and 

 hivalve molluscs only. 



t Namely, the blue rhizostome. 



t We are speakiiig here only of perfect insects. Since the researches of M. Cuvier which 

 I have at preseut in view, M. Carus has discovered in certain larvae a sort of circulation, or 

 rather a movement of the blood, which movement, however, is not effected in vessels proper. 



