166 



ANNELIDA. 



genera Serpulu, Sabella, Tertbella, Amphitrite, 

 Henrietta, and Siphostoma.) 



Third Order. ANNELIDA TERRICOLA. 

 Body, completely destitute of soft appendages. 

 Feet, scarcely or not at all distinguishable, and 



represented only by some bristles. 

 Head not distinct, without eyes, antennae, or 



jaws. 

 This order comprehends the genera Clymena, 



Lumbricus, Nais, $c. 



In the classification of M. Cuvier it is united 

 to the Hirudinida to form the order Anne- 

 lides ubranches. 



Fourth Order. ANNELIDA SUCTORIA. 

 Body destitute of bristles for locomotion, com- 

 pletely apodous, and without soft appen- 

 dages. A prehensile cavity in the form of a 

 sucker at each extremity of the body. 

 Head, not distinct, but generally provided with 



eyes and jaws. 



This order is composed of the family of Hiru- 

 dinida, and of the genus Brancliellion. 



External conformation. The Annelida have 

 always an elongated, generally cylindrical, and 

 vermicular form ; sometimes, however, they 

 are flat or more or less oval. The body is com- 

 posed, as we have already observed, of a series 

 of rings, not of a horny or calcareous texture as 

 in the majority of insects and Crustacea, but 

 membranous and separated from each other 

 only by a transverse fold of the integument; as is 

 seen in certain larvae. The number of these rings 

 is occasionally very considerable (some nereida 

 have more than 500), and in many annelida it 

 varies considerably in different individuals of 

 the same species, and seems to increase with age. 

 In some instances these segments are sub- 

 divided into two or more transverse bands by 

 furrows. 



In general each ring supports a pair of mem- 

 bers, and when an apparently single segment 

 gives origin to a greater number of these or- 

 gans, it is easy to perceive that it results from 

 the union of many rings blended together. 

 The two extremities of the body are sometimes 

 dilated in the form of suckers (in the suctorious 

 annelidans), but in general nothing of the kind 

 exists, and the anterior extremity either resem- 

 bles the rest of the body, or it terminates in a 

 head more or less distinct (as in the nereida, 

 see fg. 62), often supporting eyes (), and fili- 



Fig. 62. 



form appendages called antennas, (6,c), the num- 

 ber of which is generally three, four, or five. 



The mouth is situated at the extremity of the 

 body, and in the acephalous annelida is di- 

 rected forwards, but in the cephalous species 

 this opening is situated below the base of the 

 head. The anus is placed at the opposite ex- 

 tremity, and is almost always found on the 

 dorsal aspect of the body. A certain number 

 of Annelida are completely apodous, and do 

 not present the least trace of an appendage on 

 any of the segments of the body (the hirudinidae). 

 Others exhibit on either side many rows of 

 bristles, which fulfil the office of feet (the terri- 

 colae). In others, again, the bristles of which 

 we have spoken are supported on a fleshy 

 tubercle more or less prominent, and more or 

 less complicated in structure, and to these 

 organs the name of feet is applied. 



The feet of the Annelida, when they present 

 the maximum of development of which they 

 are susceptible in that class of animals, are com- 

 posed each of two very distinct portions, placed 

 one above the other, and appertaining the one to 

 the dorsal, the other to the ventral arch of the 

 ring. (See Jig. 63,which represents one of the feet 



of an amphinome.) M. Savigny, who was the 

 first to study with due care the zoological cha- 

 racters furnished by these appendages of the 

 annelida, gave to these portions of the feet the 

 names of dorsal oar () and ventral oar (6) (rame 

 dorsal et rame ventral). Sometimes these oars 

 are pretty distant from one another, (Jig. 63.) 

 sometimes they are separated only by a shallow 

 fissure (Jig- 64. which represents the foot of a 

 nereid), and occasionally they are so intimately 

 blended together that they can hardly be dis- 



Fig. 64. 



