CLASS GASTEROPODA. 



67 



or, in other words, from the mouth towards the apex of 

 the spire. The outer surface of the shell is of a brownish- 

 white or yellowish-brown colour, whilst the mouth is white 

 or flesh-coloured. 



Turning now to the internal anatomy of the Whelk, the 

 mouth (of the animal, not of the shell) is found 

 to contain a singular organ which is known as 

 the "tongue," and a portion of which is repre- 

 sented in a highly magnified form in fig. 28. 

 The tongue consists of a long strap, which 

 carries three rows of minute serrated teeth, 

 composed of flint. By means of proper mus- 

 cles this toothed strap can be made to move 

 backwards and forwards over a kind of cushion 

 upon which it rests. The animal can thus 

 apply it like a saw to any foreign substance, 

 and as the teeth are extremely hard, holes 

 can be bored into other shells with great readi- 

 ness. The mouth (fig. 29, a) is placed at the 

 end of a proboscis, which can be thrust out 

 to a considerable distance, and conducts by a 

 gullet to a proper digestive cavity or stomach. 

 From the stomach proceeds a long convoluted 

 intestine, in great part surrounded by a voluminous liver. 

 The intestine (c^ d) terminates in a distinct vent (e), which 

 is placed upon the back. 



The nervous system is chiefly aggregated round the 

 gullet (fig. 29, /). There is a distinct heart (h) consisting 

 of two cavities or chambers. The breathing-organs are 

 in the form of two plmne-like gUls ((/), which are 

 placed in a sort of chamber, formed by the folding 

 of the mantle, on the back of the animal. The water 

 necessary for respiration is admitted to this chamber 

 by means of the folded tube or "siphon," which has been 

 mentioned as being protruded through the notch in the 

 front of the shell. 



The common Whelk is very widely distributed through- 

 out European seas, and is one of the most abundant of 

 British Univalves. It is found usually in tolerably deep 



Fig. 28.— Por- 

 tion of the 

 tongue of the 

 Whelk, high- 

 ly magnified 

 (after Wood- 

 ward). 



