A MANUAL 



LAND AND FRESH-AVATER MOLLUSCA 



THE BRITISH ISLANDS. 



MoLLUSCA is tlie name given to that large division 

 of the animal kingdom which is characterised by 

 having a soft fleshy body, destitute both of a bony 

 skeleton supporting jointed limbs, and of a hard 

 ringed skin. 



They are covered with a muscular coat, called a 

 mantle, endued with a glairy humour, and are gene- 

 rally furnished with a calcareous envelope called a 

 shell, which is secreted by this coat for the protec- 

 tion of the body or of the more vital organs of the 

 animal. 



They are usually elpngate, walking on a single 

 central foot or disk, and are furnished with one or 

 more pairs of organs on the head and sides. Their 

 nervous system, which affords the most distinctive 

 character of the larger groups of the animal king- 

 dom, merely consists of a certain number of medul 

 ^V B 



