178 M. Deshayes' Monograph of Dentalium. 



derably larger than those of the anterior. In the centre of the anterior 

 lip is a naked space indicating the opening of the mouth, which contracts 

 into a short fleshy oesophagus, terminating quickly in a pyriform thick 

 stomach, supported by, and firmly adhering to, the extremity of the foot, 

 and containing in its interior, near the cardiac opening, a rather compli- 

 cated dentary apparatus. The stomach receives directly by a distinct ves- 

 sel from each of the symmetrical lobes of the liver already noticed its 

 secretion, and terminates inferiorly in a slender transparent, straight, me- 

 dian intestine, opening at the dilated posterior extremity. 



Of the general circulation little has yet been observed. The heart is 

 symmetrical, and is placed above the stomach, being contained in a pyri- 

 form pericardium. Issuing from the anterior extremity of this sac is seen 

 a vascular trunk, passing in the direction of the neck, and dividing into 

 two large branches, one of which is distributed to each of the branchiae. 

 These latter organs are two in number, and are symmetrically placed on 

 the lateral and posterior parts of the neck, being supported on a divided 

 pedicel, or rather on a branchiferous membrane. They are formed by a 

 multitude of very fine, soft, flexible, tentacular filaments, the terminations 

 of which are club-shaped, and appear from their position equally adapted 

 to direct the nutritive matter towards the mouth, and to fulfil their more 

 important office of supplying oxygen to the blood. 



The organs of generation are still less known ; no male organ having 

 been discovered, nor any female one except the large ovary, which fills 

 nearly the whole of the abdominal cavity, but of which even the exter- 

 nal opening remains yet to be discovered. 



The nervous system, so far as it has yet been traced, appears to be gan- 

 glionic ; at least there exists, according to M. Deshayes, no longitudinal 

 knotted marrow. The cerebral ganglion, the only one yet observed, is 

 small, quadrilateral, much elongated, and placed longitudinally on the 

 middle of the posterior surface of the head. From its inferior angles 

 issue two very minute filaments, which pass to the oesophagus, beyond 

 which they have not been traced. 



Such are the anatomical materials furnished to us by M. Deshayes. 

 Confessedly imperfect as they are, they are still extremely interesting, as 

 demonstrating, if the account of the nervous system be correct, that the 

 genus Dentalium can no longer be referred to the Annulose type of the 



