ANNELIDES. 



83 



certain number of conical or filiform appendages, which we distin- 

 guish into antennae, palpi, and tentacula. The antennae are directly 



No. VII. 



attached to the head, and their insertion is always superior (fig. 1, o ; 

 fig. 2, b). The palpi are more connected with the mouth, and their 

 insertion is inferior (fig. 1, b b)*. The tentacula (fig. 1, c c) are 

 filiform organs inserted, in pairs, on each side of the head, and of 

 the post-cephalic segment, when this is apodous. 



4. Mouth. — In the Annelides with a head obscurely defined, as, 

 for example, in the Tubicoles, the mouth is usually terminal ; but 

 in all the cephalous genera it is on the ventral or inferior aspect. 

 It is either a simple wide aperture, or it is furnished with a proboscis 

 (fig. I and fig. 2, e, e), which can be extruded at the will of the 

 animal, although it is kept retracted and concealed in the state of 

 quiescence. It may be considered as simply a portion or continua- 

 tion of the alimentary canal. It is often armed with horny jaws 



however, that they do not contain any transparent parts, and are not furnished 

 with any optical apparatus: they are simple swellings of the optic nerves, sur- 

 rounded with a black pigment, sensible to light, and enable the worm to distin- 

 guish between light and darkness, — between places which lie in shade and those 

 which are exposed to the glare of day ; but not imparting the power of recog- 

 nizing the shape, or colour, or texture of bodies. — Ann. des Sc. Nat. tom. xxii. 

 p. 25. See also in favour of their being eyes, Bourjot in Microsc, Journ. i. 

 p. 77 ; and Cuvier in Analyse des Travaux de I'Acad. Roy. des Sc. 1828, p. 82, 

 &c. ; De Quatrefages in Ann. des Sc. Nat. iv. (1845) p. 178. But M. de Quatre- 

 fages has found in some species, especially in Torrea vitrea, eyes that have a 

 crystalline lens, a choroid coat, a vitreous humour, a transparent cornea, &c. 

 " Some Annelida have other eyes besides those on the head. M. Quatrefages 

 beheves that he has discovered them upon the branchiae of the Sabellae, and he has 

 no doubt that the red points which we find upon the sides of each ring in several 

 Annelida of the genus Nais are true eyes ; there is, however, nothing surprising 

 in this, when we recollect the very great independence existing between the 

 various rings of which the body of these animals consists." — Ann. & Mag. Nat. 

 Hist., Ser. 2. vi. p. 228. 



* Audouin and Milne-Edwards call the central organs median antenna?, and 

 the palpi external antennae ; but our nomenclature does away with the adjective, 

 and the structure of the organs would seem to indicate a difference in their 

 functions. 



g2 



