194 



THE SEA SHORE 



their circumferences towards the urnbo, to which they all converge. 

 These lines enclose the areas previously occupied by the muscular 

 impressions ; in other words, they show the directions in which the 

 muscles named above shifted their positions as the animal grew. 



Now let us obtain a few species of live lamellibranchs, put 

 them in a vessel of sea water, and observe them after they have 

 been left undisturbed for a time. The shell will be seen to gape 

 slightly, exposing the edges of the two lobes of the mantle which 

 lie closely on the inner surface of the valves, thus completely 

 enveloping the body of the animal; and at one end, usually the 

 narrower end in the case of irregular shells, we shall observe two 



FIG. 129. DIAGRAM or THE ANATOMY OF A LAMELLIBBANCH 



/, mouth, with labial palps ; g, stomach ; i, intestine, surrounded by the liver ; 

 a, anus: r, posterior adductor muscle; e, anterior adductor muscle; c, heart; 

 (I, nerve ganglion ; m, mantle (the right lobe has been removed) ; s, siphons ; h, gills ; 

 ft, foot 



openings the siphons, sometimes enclosed within a tube formed 

 by a prolongation of the united mantle lobes, and protruding from 

 between the valves, and sometimes formed by the mere contact 

 of the mantle lobes at two adjacent points. If now we introduce 

 a little carmine or other colouring matter by means of a glass tube, 

 setting it free near the lower siphon the one more remote from 

 the umbo of the shell, we observe that it enters the body of the 

 mollusc through this opening, and reappears shortly afterwards 

 through the upper or dorsal siphon. Thus we see that water 

 currents are incessantly circulating in the body of the animal, 

 entering by the inhalent or ventral siphon, and leaving by the 



