126 ANNELIDKS. 



sects; for as the nutritive fluid is not contained in vessels*, and 

 could not be directed toAvards pulmonary organs in search of air, it 

 was requisite that this air should be diffused throughout the body to 

 reach the fluid. This is also the reason why insects have no secretory 

 glands, but are provided with mere spongy vessels, which, by the 

 extent of their surface, appear to absorb the peculiar juices they are 

 to produce, from the mass of the nutritive fluid f . 



Insects vary infinitely as to the form of the organs of the mouth, 

 and those of digestion, as well as in their industry and mode of life ; 

 the sexes are always separated. 



The Crustacea and Arachnides were long united with the Insecta, 

 under one common name, and resemble them in many points of their 

 external form, in the disposition of their organs of motion, and of 

 the sensations, and even in those of manducation. 



CLASS I. 



ANNELIDES:. 



The Annelides are the only invertebrate animals that liave 

 red blood. It circulates in a double system of complicated 

 vessels §. 



Their nervous system consists in a double knotted cord, like that 

 of insects. 



Their body is soft, more or less elongated, and divided into a, fre- 

 quently, considerable number of segments, or at least of transverse 

 plicae. 



They nearly all inhabit the water — the Lumbrici or Earth-worms 

 excepted ; several penetrate into holes at the bottom, or construct 



* M. Carus has observed regular movements in the fluid which fills the bodies of 

 certain larvse of Insects ; but this movement does not take place in a system of 

 closed vessels, as in the superior animals. See his treatise entitled " Discovery of a 

 simple circulation of the blood, &c." in German, Leipsic, 1827, -ito. 



t On this subject see my Memoir on the nutrition of Insects, printed 1799. 

 Mem. de la Soc. d'Hist. Nat. de Paris. Baudouin, an vii, 4to, p, 32. 



X I established this class, distinguishing it by the colour of its blood and other 

 attributes, in a Memoir read before the Institute in 1802. See Bullet, des So., 

 Mesidor, an X, where I described the organs of the circulation. 



M. Lamarck has adopted and named it, Annelides. Brugicres previously united 

 it to the order of the intestinal worms, and before him, Linnaeus placed part of these 

 animals among the Mollusca, and the rest among the Intestini. 



§ It has been asserted that the Blood of the Aphrodita is not red. I think I 

 have observed the contrary in the Aphrodila squamafa. 



