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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 suiTounding parts, and 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 Articulala into four Classes. 
I’lie 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 
mouth 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 
ovum of 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. Rathkc on that of the Astaci, Leipsic, 1829. 
