RINGED-WORMS. 217 



Nereidce QUATREFAGES found this system to be composed of differ- 

 ent ganglia, and named it, on account of its position on the pro- 

 boscis, systime susoesophagien, or proboscidian superieur 1 . 



With respect to organs of sense, with the exception of tentacles 

 and other appendages subservient to a finer sense of touch, for sight 

 there are found in most species only coloured spots, usually black, 

 of variable number, as special organs. According to I. MUELLER'S 

 investigations in a Nereis, the eyes of ringed-worms contain no 

 transparent parts, but are merely swellings of the visual nerves sur- 

 rounded by black pigment. They are endowed with sensibility for 

 light, and the worms can distinguish between light and darkness : 

 but what is properly named sight, perception of the form of objects, 

 such eyes cannot afford. In Alciopa lepidota KROHN however found 

 a lens and a vitreous body. A special auditory organ has not been 

 detected ; the first portion of the oesophagus is supposed to be the 

 seat of taste. 



The organs of motion are in some more complicated than in 

 others. In all muscular fibres are found beneath the skin, which 

 may be separated more or less completely into layers : the external 

 layer has a circular, the internal a longitudinal course. In some, as 

 Aphrodite, these fibres are united to form distinct bundles. By means 

 of the layers or bundles the body can be moved, contracted, extended, 

 bent. Besides this general muscular system, motion of the body 

 in the Leech can be also effected by means of a suctorial disc at its 

 posterior part, in which there are circular and radiating fibres. The 

 proboscis, which is capable of eversion and retraction, has proper 

 muscles for these purposes. Concerning the bristles and hairs, 

 which are found on many, we have already spoken above. These 

 parts, springing from the sides, supply fixed points for the motions 

 of the body, like the spines of the Echini: they are retracted, ex- 

 tended or moved sideways by proper muscles. 



Many species of this class diffuse a phosphoric light. It is 



1 There lies also a small ganglion in front of the brain (ganglion cervical QUATRE- 

 FAGES), and from the lateral parts of the brain a thread arises, which with that of the 

 other side surrounds the mouth (Systeme sous-cesophagien labial au proboscidien 

 inferieur) ; this last portion of the nervous system may be compared with the arrange- 

 ment in the Mollusca gasteropoda. See on the nervous system of the Annelids 

 a memoir of QUATREFAGES illustrated with beautiful figures, Ann. des Sc. not. 30 SeVie, 

 Tom. II. Zoologie, 1844, pp. 81 104. 



