124 ARTICULATA. 



at certain distances by double knots or ganglia, whence arise the 

 nerves of the body and limbs. Each of these ganglia seems to fulfil 

 the functions of a brain to the surrounding parts, arid to preserve 

 their sensibility for a certain length of time, when the animal has 

 been divided. If to this we add, that the jaws of these animals, 

 when they have any, are always lateral and move from without, in- 

 wardly, and not from above, downwards, and that no distinct organ of 

 smell has hitherto been discovered in them, we shall have expressed 

 all that can be said of them in general. The existence, however, of 

 the organs of hearing, and the existence, number and form of those of 

 sight, the product and mode of generation*, the kind of respiration, 

 the existence of the organs of circulation, and even the colour of the 

 blood present great differences, which must be noticed in the various 

 subdivisions. 



Distribution of the Articulata into four Classes. 



The Articulata, whose mutual relations are as varied as numerous, 

 present however four principal forms, either internal or external. 



The ANNELIDES, Lam., or RED-BLOODED WORMS, Cuv., constitute 

 the first. Their blood, which is generally red, like that of the 

 Vertebrata, circulates in a double and closed system of arteries and 

 veins, sometimes furnished with one or several visible hearts or fleshy 

 ventricles. Respiration is performed in organs which are sometimes 

 developed externally, and at others remain on the surface of the 

 skin or dip into its interior. Their body, more or less elongated, is 

 always divided into numerous rings, the first of which, called the 

 head, scarcely differs from the rest, except in the presence of the 

 month and the principal organs of the senses. The branchiae of 

 several are uniformly distributed along their body or in its middle ; 

 in others, which are generally those that inhabit tubes, they are all 

 placed anteriorly. They never have articulated feet, but most of 

 them, in lieu thereof, are furnished with setae or fasciculi of stiff and 

 movable hairs. They are mostly hermaphrodites, and some of them 

 require a reciprocal coitus. The organs of their mouth sometimes 

 consist in jaws, more or less strong, and at others of a simple tube, 

 those of the external senses in fleshy, and sometimes articulated ten- 

 tacula, and in certain blackish points, considered as eyes, but which 

 do not exist in all the species. 



* M. Harold has made a remarkable discovery on this subject, viz. that in the 

 ovumof the Crustacea and Arachnides, the vitellus communicates with the interior 

 by the back. See his Dissert, on the ovum of Spiders, Marburg, 1824, and that of 

 M. Rathke on that of the Astaci, Leipsic, 1829. 



