34: 



BRANCH MOLLUSCA. 



FIG 46. 



FIG. 47. 



are not capable of extending from between the edges of 

 the shells, which are 

 placed one above and one 

 below the animal. In the 

 Lamp-shell of the New 

 England coast, these shells 

 are united posteriorly by 

 a hinge, while projecting 



Ter e brat u H'na 



sep ten tn o ml'lis. 



Lamp-shell. 



from the larger is a short 



Tongue-shell. 8, Peduncle, 



the lower end of wbicl1 



is anchored in the sand. 



peduncle (pe dting'kl), 

 which serves to hold the animal to 

 some support. The Tongue-shells, of 

 more southern waters, are without this hinge, but have 

 the peduncle greatly elongated, anchoring the animal 

 uprightly in the sand. 



BRANCH MOLLUSCA ( msi 



CLAMS, SNAILS, ETC. 



This Branch includes animals of which the Clam, Snail, 

 and Nautilus, are examples. The soft body is surrounded 

 by a mantle, which generally secretes a limy covering, 

 protected externally from the erosive action of the water 

 by a thin, horny layer the epidermis (ep i der'mis). The 

 body is bi-symmetrical, though in some forms, a torsion 

 interferes with exact symmetry. The alimentary tract is 

 completely separated from the body cavity, the nutritive 

 fluid being carried over the body, and through the gills, 

 where it is purified, by a system of blood-vessels, which 

 lead to and from a muscular heart. The nervous system 

 is well developed and regularly disposed. Three classes 

 are distinguished. 



