SUPPLEMENT. 



585 



CLASS ANNELIDES. 



This class is the first of the great division 

 Articulata, consisting of animals which have 

 their bodies or members composed of articu- 

 lated rings. The characters of the Annelides, 

 are, the body soft, more or less elongated, and 

 either naked or enclosed in a tube, and divided 

 into a number of segments ; and are the only 

 animals devoid of a backbone, which have red 

 blood circulating in a double system of com- 

 plicated vessels. Their nervous system con- 

 sists in a double knotted cord, like that of 

 insects. Some species have a head, and others 

 are devoid of one ; when it exists it is merely 

 a slight anterior thickening, distinct from the 

 first segment of the body, and upon which the 

 eyes and antennae are placed. The antennas 

 consist of articulated filaments, sometimes short 

 and thick, a?nd never exceed five. They have 

 either two or four eyes, situate behind the an- 

 tennae. The tentacula are either situated on 

 the head or fore part of the body, they consist 

 of articulated filaments, or papillae more or 

 less elongated. They are provided with a 

 fleshy contractile proboscis, of either one or 

 two rings, inclosing horny or calcareous jaws. 

 The body of the Annelides in many species 

 is naked, and free from hairs ; some are fur- 

 nished with contractile bristles. The whole 

 class respire by branchiae, and inhabit the 

 waters, sand, mud, or moist earth. The bran- 

 chiae are extremely variable in form and situa- 

 tion ; as are also the tubes or sheaths, which 

 are either membranous or horny, incrusted 

 exteriorly with minute fragments of shells or 

 grains of sand ; in others they are solid testa- 

 ceous tubes. They are all carnivorous, suck- 

 ing the blood of other animals ; and are her- 

 maphrodite. 



ORDER I. SEDENTARY. 



The animals inhabit a testaceous tube, which they 

 never leave; they are destitute of eyes; the branchiae 

 are situated at one end of the body. The animal is 

 elongated, worm-shaped, having the sides of the body 

 provided with subulate short bristles; and also with 

 hooked bristles to enable it to move in its tube. 



FAMILY I. SERPULACEA. 



Branchiae separate, or covered by an operculum; tube, 

 solid and testaceous; destitute of tentacula, eyes, or 

 jaws ; body furnished on the sides with setaceous pa- 

 pillse, and hooked retractile bristles. Serpula vermicu- 

 laris, pi. 24, f. 82. 



FAMILY II. AMPHITRIT^EA. 



Branchiae neither separated nor covered by an oper- 

 culum, and disposed towards the anterior part of the 

 body ; with a horny or membranous tube, more or less 

 arenaceous; the branchiae are placed at or near the 



VOL. II. 



anterior extremity, they are sometimes large, project- 

 ing above the mouth, and sometimes they are short. 

 Many of the animals have tentacula, but all of them 

 are destitute of eyes, proboscis, or jaws. Amphitrite 

 magnified, pi. 24, f. 81. 



FAMILY III. MALDANI.E. 



The branchiae are indeterminate; and the tube is open 

 at both ends. Dentalium entails, 



FAMILY IV. DORSALI^E. 



The branchiae are dorsal, or disposed longitudinally 

 along the body. Siliquaria anguina, pi. 33, f. 51. 



ORDER II. ANTENNAT/E. 



The head is antenniform, provided with two eyes, 

 and a projectile proboscis, frequently armed with jaws, 

 and setiferous retractile pediform papillae; branchiae 

 disposed longitudinally. 



SECTION I. 



Branchiae in the form of complicated leaves or tufts, 

 or very ramose, always large and apparent; destitute of 

 spines. 



FAMILY I. AMPHINOM^G. 



Branchiae and cirri placed superiorly at all the pairs 

 of pediform papillae, and having no jaws. 



SECTION II. 



Branchiae in the form of small crests or laminae, or 

 filamentous and pectinated on one side; sometimes not 

 distinct. 



FAMILY II. EUNICE. 



While the branchiae are distinct, all the pediform 

 papillae are placed without interruption ; jaws numerous, 

 and always more than two, but fewer on the right than 

 on the left side; destitute of the first pair of feet. 



FAMILY III. NEREIDES. 



When the branchiae are distinct, there are superior 

 cirri on all the pairs of pediform papillae; two jaws or 

 none. Spio quadricornis, pi. 27, f. 14. 



FAMILY IV. APHRODITE. 



The upper branchiae and cirri alternating in their 

 position to the twenty-third or twenty-fifth pair of 

 pediform papillae; having four jaws. Halitliea aculeata, 

 pi. 27 f. 4. 



ORDER III. APODES. 



Animals destitute of feet, or setiferous and retractile 

 papillae ; when provided with branchiae, they are dis- 

 posed interiorly along the body; but they have no an- 

 tenniferous head. Although the animals of this order 

 have red blood, and a true circulation, they are other- 

 wise the most imperfect in their form. They are des- 

 titute of head, tentacula, and pediform papillae; their 

 branchiae are situated internally, either in or under the 

 skin. They are usually naked, and have no retractile 

 spines. 



FAMILY I. ECHIURE.E. 



Body with bristles projecting, but not retractile. 

 Lutnbricus terrestris, pi. 27, f. 39. The earth worm. 



FAMILY II. HIRUDINE.E. 



Body without projecting bristles. Hirudo geometra, 

 pi. 27, f. 13. Leech. See it described in the present 

 volume, at p. 467. 



4 B 



