4 EAMBLES IN SEAKCH OF SHELL'S. 



end of the ribbon can work backwards and forwards, 

 so as to rasp and triturate the food between them. 

 The tubular portion of this lingual ribbon is* con- 

 tained in a cavity behind the mouth, and as the 

 teeth in use become worn or broken, it is con- 

 jectured that they are absorbed, and a fresh set 

 from the reserve in the tube is pushed forward to 

 take their place. 



The body of every mollusk with which we are con- 

 cerned, except those of the slug family, is contained 

 in a membranous sac called the mantle, which not 

 only serves as a model on which the shell is moulded, 

 but is liberally provided at the edges of its open end 

 with the glands that secrete the shelly matter. To 

 this set of glands alone are due the coloured bands 

 and other markings in the shells, as may be seen in 

 the case of a fractured specimen that had been 

 repaired by the owner ; in this, the new matter 

 thrown out of the mantle under the fracture is 

 always colourless. 



Some curious observations on the growth of shells 

 of land snails were communicated by Mr. E. J. Lowe, 

 to the Royal Society in 1854. He found that the 

 shells of Helices increase but little for a con- 



