ANNELIDA. 167 



languished, and form, as it were, but a single enclosed in tubes formed by the mucus which 

 organ ; lastly, there are cases in which only is secreted by the skin, and which, while hard- 

 one of the oars would seem to be developed, ening, commonly agglutinates together frag- 

 If one were disposed to compare the loco- ments of shells and sand. The formation of 

 motive system of the annelida with that of the these sheaths is very quick. I have seen them 

 other articulate classes, the ventral oar should be fabricated in the course of a few hours. Some- 

 regarded as analogous to the members which in times they are of extreme tenuity, occasionally 

 the Crustacea, Insects, &c. are variously modified they are as tough as thick leather, and there 

 to constitute the legs, the jaws, or the antennae : are some which possess very considerable 

 and the dorsal oar ought to be considered as hardness and are composed in great proportion 

 representing the appendages, which, though of carbonate of lime, like the shells of mol- 

 wanting in the greater number of articulate lusca. In the greater part of these animals 

 animals, yet acquire a considerable develop- locomotion is produced by general undulations 

 ment on the last two rings of the thoracic of the body determined by contractions of a, 

 segment of most insects and constitute the layer of muscular fibres extending from one 

 wings. In this particular the annelida afford ring to another, and fixed to the inner surface 

 an example of the greatest uniformity in the of the skin. But in other species the change 

 development of the appendicular system in the of place is effected by the action of the feet, 

 articulate division of the animal kingdom. of which we have spoken ; or by the contrac- 



Each oar is essentially composed of a fleshy tion of the tentaculae which surround the 



tubercle more or less prominent, which sup- mouth, as in the terebellae, and which, by 



ports different productions of the integument, shortening themselves, drag on the body of 



incloses the bristles (c), and which is more the animal in the same manner as the arms of 



especially designated by the name of foot, the cephalopods : lastly, by the action of the 



Towards the base of the setiferous tubercle suckers with which the extremities of the body 



there is generally a membranous appendage, are furnished. 



sometimes filiform, sometimes lamelliform, The bristles (fig. 63 and 64, r,) with which 

 called the cirrus (d, e) ; lastly, it is also above the feet of the annelida are provided, do not serve 

 the margin and near the base of these organs merely as little levers to facilitate their move- 

 that the branchiae (f) take their origin, but in ments, but are also offensive arms, and their 

 general it is only the dorsal oar that supports structure is very curious. They differ con- 

 them. All the above parts may exist simul- siderably from the hairs of other articulate 

 taneously, but it often happens that one or animals, which are nothing more than small 

 more are atrophied to a greater or less degree, tubular prolongations of the epidermic layer, 

 or are altogether deficient ; and this either By their mode of connexion with the integu- 

 along the entire body or on certain segments ments and their mode of formation they ap- 

 only. Thus in the terricolous annelida there pear to approach the hair of mammalia, but 

 are no cirri ; in the hermellae they are pre- their disposition is of a more complicated na- 

 sent on the ventral, but not on the dorsal oar ; ture. They are inclosed in sheaths provided 

 while in the cirrhatulae the reverse obtains. with muscular fibres, by the aid of which the 



In most of the annelida errantia the setiferous animal can protrude and retract them again : 



tubercle of both oars is wanting on the first in general, also, they are not merely simple 



rings which follow the head, whilst the cirri conical filaments, but their extremity is often 



assume a very great development, and form the shaped like a harpoon, a lance, or a barbed 



appendages termed by systematic authors ten- arrow, and the annelidan uses it to inflict a 



tacular cirri. (Fig. 62, d.} wound upon its enemies.* 



A similar modification may be frequently Sensation. Tactile sensibility is considerable 



remarked in the composition of the appen- in these animals, and it seems to reside prin- 



dicular system of the last ring of the body, and cipally in the antennae, the cirri, and the 



thence results a certain number of filiform pro- tentacula. They do not appear to possess a 



ductions called styles. Lastly, the antennae of sense of hearing, and there are many among 



the annelida, which must not be confounded them which do not manifest any sign of sen- 



with the antennae of insects and Crustacea, may sibility to light ; but in others, eyes (Jig. 62, ,) 



also be considered as representing the cirri of exist, the number of which is sometimes very 



the dorsal oar of those rings, the union of which considerable, but the structure very simple, 



constitutes the head.* They are coloured points, (generally black,) and 



The annelida pass in general a somewhat situated on the dorsal aspect of the head or on 



stationary life, and a great number among the cephalic sucker. In the setiferous anne- 



them remain constantly buried in the earth or lida there are never more than two pairs, but 



in the hirudinidae or leeches their number 



?or further details regarding the external stmc- o f ten increases to eight or ten. The anatomy 



tare 01 the annelida the reader mav consult thp / xi. i ^11. j- i i_ 



excellent work of M. Savigny, intitled << %steme * ese IX^JZSfi T \ * 



des Annelides," principally of those found on the Professor Muller of Berlin, and according to 



coasts of Egypt and Syria; the article ' Vers ' of his researches it would seem that these organs 



the Dictionnaire des Sciences Naturelles, torn. Ivii. do not contain a crystalline lens, or a trans- 



ilamville; and a more recent publica- parent body analogous to the vitreous cones of 

 on on the same subject inserted in the Annales 

 des Sciences Naturelles, torn, xxviii, xxix, and xxx, 



and in the second volume of the Recherches pour * See Observations sur les Foils des Annelides 



Hist. Nat. du littoral de la France, par considered comme moyen de Defense, par MM. 



VI. Audouin ct Milne Edwards.' A udouin et Milne Edwards, op. cit. torn. ii. p. 31. 



