774 ARTICULATA— ANNELIDES. 



DIVISION III. — ARTICULATA. 



* 



The third great division of the animal kingdom consists of animals whicti 

 have their body or members composed of segments or articulated rings, to 

 the interior of which the muscles are attached. The nervous system con- 

 sists of two long chords extending along the belly, and swelled out at inter- 

 vals into knots or ganglia. The first of these placed upon the oesophagus, 

 tnough but little larger than the others, is considered as analogous to the 

 brain in the higher animals. The teguments of the body are sometimes 

 hard, sometimes soft; and the trunk has often at its sides articulated mem- 

 bers, though in some groups these are wanting. As formerly observed, it is 

 m this division of the animal kingdom, that the transition of the circulation 

 in closed vessels to nutrition by imbibition is observed; and the correspond- 

 ing transition from respiration in circumscribed organs, to that performed 

 by trachea, or air vessels distributed through the body. The organs of 

 movement and sense are disposed symmetrically on the sides of a common 

 axis. The senses of taste and sight seem most distinct; and their jaws, 

 when they have any, is always lateral. This division of the animal kingdom 

 contains five classes, viz : — annelides, Crustacea, arachnides, mtriafoda, 

 and insecta. 



CLASS V.— AN N E LIDE S. 



Body soft, more or less elongated, naked or inclosed in a lube, and divided into 

 a number of segments ; blood red. 



The animals of this class are the only invertebral ones which have red 

 blood, circulating in a double system of complicated vessels. Their body is 

 naked or inclosed in a tube, formed of segments, or transversely wrinkled, 

 and often without a head, eyes, or antennae. They are destitute of articu- 

 lated feet ; but the greater portion have in their place, setiferous, retractile 

 papillae disposed in lateral rows. The mouth is nearly terminal simple, 

 "rbicular, or labiated, or in the form of a inaxinary proboscis. The anatomi- 

 cal structure of the animals of this class has been investigated by Cuvier, 

 Montegre, Spix, and Savigny ; and the result of their observations has led to 

 tYieir arrangement in a separate group. The animals of this group, it may 

 be remarked, formed part of the class Vermes, of Linnaeus. 



The head of these species which are provided with one, is a slight anterior 

 thickening, distinct from the first segments of the body, and upon which are the 

 antennae and eyes. The antennae are articulated filaments, sometimes short 

 and thick, inserted on the head, and of which the number exceeds five. 

 The eyes, to the number of two or four, are also upon the head, behind the 



