Miscella neoiis. ^87 



and the base of the foot ; tliey form a new circle which embraces the 

 whole base of the foot and the dijjestive apparatus. The anus always 

 remains beyond this. The ganglia being generally close together, 

 there is only one distinct commissure, that which unites the two pos- 

 terior ganglia, passing in front of the anus. 



This arrangement of the nervous system reminds one of that of 

 the lamellibranchiate Acephala : there are two collars attached to the 

 supra-fcsophageal ganglia, — one anterior, terminating with the pedal 

 ganglia, — the other posterior, and completed by the posterior ganglia 

 and their commissure. The mouth is surrounded by the former ; the 

 anus, on the contrary, is behind and without the second, as in the 

 Acephala. 



The organs of special sense are the otolitbes and the tentacles. 

 The otolithes, formed by two small transparent vesicles containing a 

 great number of small calcareous corpuscles (soluble with effervescc-nce 

 in nitric acid) constantly agitated by the movements of the vibratile 

 cilia of the walls, are attached to the back of the pedal ganglia. 



The very numerous tentacular filaments, placed in the vicinity of 

 the mouth and forming two tufted branches, appear to be organs of 

 touch, and perhaps of prehension, like those on the heads of some 

 Annelides. The cutaneous fold which bears them receives a very 

 voluminous nerve which is distributed in its interior and furnishes 

 numerous branches ; there is no part of the animal so richly provided 

 with nervous tilaments. The tentacles themselves possess so much 

 contractility and execute such varied movements that they might be 

 taken for twisted worms, and their extremities are clavate and fur- 

 nished with a cavity which forms a true sucker. From this cavity, 

 which is clothed with vibratile cilia, a canal penetrates into the fila- 

 ments, but the author has been unable to follow it far. Dentalia 

 placed in small glass vessels protruded their filaments and fixed them 

 to the walls. There are no apparent organs of vision. 



The stomato-yastric or sympathic nervous system exists in Den- 

 tal ium. It arises from the buccal nerves furnished by the same 

 supra-cesophageal ganglion by two roots, one right, the other left. 

 These two roots run backward towards the lingual musculo-cartilagi- 

 nous mass, become inflated into two small ganglia united by a trans- 

 verse commissure, then continue their course, rising towards the back, 

 become inflated again into two small ganglia also united by a transverse 

 commissure, and lose themselves in the digestive canal. The lingual 

 apparatus is thus surrounded by a network formed by the commis- 

 sures, the roots and the branches arising from the secondary ganglia. 

 Towards the middle the first commissure furnishes a single branch 

 which penetrates into the lingual apparatus from its lower surface. 



Tiie nervous system ofDentalium is therefore much more complete 

 than was supposed. The division of Cirrhibranches formed by 

 Blainville, in accordance with the interpretation given by Deshayes 

 to the tentacular filaments, is much compromised if these filaments, 

 instead of being branchise, are organs of touch, and it will also be 

 diflficult to admit the ojjinion of Mr. W. Clark, who regards them as 

 salivary glands. — Comjjfes Rendus, April 27, 1857, p. 864. 



