MOLLUSCA. 189 



TEREBRATULA. Valves unequal, the peduncle passing 

 through an aperture in the largest valve. 



The following interesting information, from the dissec- 

 tions of Mr. Owen, will be read with pleasure by the student 

 of the anatomy and physiology of the mollusca. 



The mantle adheres very closely to the valves : the lobe 

 which corresponds to the perforated valve is traversed longi- 

 tudinally by four large vessels ; the opposite lobe is simi- 

 larly traversed by two such vessels. Its margins are thick- 

 ened, not as in the Lamillibranchiate Bivalves from con- 

 traction, but owing to a peculiar structure connected with 

 respiration. They are puckered at regular distances, the 

 puckerings being apparently caused by the insertion of de- 

 licate cilia, which pass as far within the mantle as they pro- 

 ject out of it, but which are so minute as to be observable 

 only by means of a lens. In the interspaces of the cilia the 

 margin of the mantle is minutely fringed, and within the 

 fringe is a canal, which extends along the whole circumfer- 

 ence. From this canal the large vessels of the mantle lobes 

 take their origin : they may be regarded as the branchial 

 veins conveying the aerated blood to the two hearts, which 

 are situated exterior to the liver, and just within the origin 

 of the internal calcareous loop : they are accompanied in 

 their course by much smaller vessels, probably the branchial 

 arteries. Such is apparently the system of respiration in 

 Terebratula. 



The viscera occupy a very small space near the hinge. 

 The alimentary canal commences by a small puckered 

 mouth, situated immediately between the folded extremi- 

 ties of the arms. It passes backwards, and expands into a 

 membranous stomach, surrounded by the liver, a bulky gland 

 of a green colour and minute follicular texture, which com- 



