64 Elementary Zoology. 



which is divided into a dorsal softer part, containing the viscera, 

 and a muscular projection below and in front, which is termed 

 \hQ foot. This latter is the organ of progression, and in some 

 lamellibranchs is so active in its movements that the animal 

 can execute considerable leaps ; this is the case with the 

 common c"bckle. The movements of anodon, however, are 

 lethargic. The most prominent organs seen are the gills, 

 which have a fenestrated, lattice-like appearance; they are 

 posteriorly continuous with the septum already spoken of, 

 which divides the inhalent from the exhalent orifice at the 

 posterior end of the body. Each of the two gills of each side 

 of the body is really a bag which, in the case of the outer gill, 

 is attached along both its edges to the body-wall; the inner 

 gill, on the other hand, is open at various points, the inner 

 lamella not being continuously attached to the body-wall. 



In front of the gills, and at the sides of the mouth-opening, 

 which latter lies above the foot, are a pair of ribbed flat plates, 

 not unlike the gills in colour and appearance; these are the 

 labial palps. The only other structures which are visible 

 without further dissection are the various muscles already, 

 spoken of in describing their impressions upon the shell. If 

 the two lamellae of the inner gill be widely separated by cutting 

 through the inner lamella and turning back the cut edge, the 

 openings of the renal organs and the generative gland will be 

 found close to each other. These apertures lie upon the body- 

 wall between the attachments of the two lamellae of the inner gill. 



The alimentary canal of the mussel is simple. The mouth, 

 just behind the anterior adductor, leads into a short cesophagus, 

 which in its turn opens into a somewhat globular stomach (stm), 

 into which debouch the bile-ducts, carrying thither the secretion 

 of brown and much-branched liver. The intestine (int) coils 

 in the substance of the upper part of the foot, and then, 

 rising towards the dorsal surface of the body, runs a straightish 

 course through the pericardial cavity to the anus, which is 

 placed at the end of a slight papilla in the exhalent chamber. 



The pericardial chamber is so called on account of the fact 

 that it lodges the heart. . It is practically all that exists of the 

 calom in this animal, which is thus much reduced as compared 



