244 



PALAEONTOLOGY. 



figure a shows the mature, and figure b the immature shell. 

 This important fact should be recollected by the young 

 naturalist. For further details on the anatomy of the shell, 

 we refer to fig. 165, and the description thereof. 



The mouth is surrounded by fleshy contractile lips, some- 

 times armed with teeth. We observe in some a singular 

 file-like organ, which extends into the intestinal canal. It is 

 formed of a ribbon-like membrane, which develops a series 

 of tooth-like processes, the form and disposition of which 



FIG. 166. Cyprvecdssis rii/a; a, mature ; b, immature. 



vary in the different genera. These palates, as they are 

 called, form beautiful microscopic objects, when neatly dis- 

 sected out and mounted in Canada balsam. Those of bucci- 

 num, nerita, patella, chiton, and doris are interesting objects 

 when viewed by polarised light. 



The stomach is capacious, and is often armed with calca- 

 reous plates for dividing the food. The intestine is coiled 

 upon itself, and lies between the lobes of the liver and ovary, 

 and terminates in an anal aperture. 



