ARTICULATA. 291 



The system of organs in which the Articulata resemble each other 

 the most, is that of the nerves. 



Their brain, which is placed on the oesophagus, and furnishes 

 nerves to the parts adhering to the head, is very small. Two cords 

 which embrace the oesophagus are extended along the abdomen, 

 and united 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, 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 inwardly, and not from above downwards, and that no dis- 

 tinct organ of smell has hitherto been discovered in them, we shall 

 have expressed all that can be said of them in general. The exis- 

 tence however of the organs of hearing, the existence, number and 

 form of those of sight, 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 numer- 

 ous, present however four principal forms, either internal or ex- 

 ternal. 



The ANNULATA, Lam., or RED-BLOODED WORMS, Cuv., consti- 

 tute 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 elon- 

 gated, 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 on its mid- 

 dle; 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. The organs of their mouth sometimes consist 



