CHAPTER IV. 



THE BRANCH OF MOLLUSCA, OR MOLLUSKS. 



THE Branch of Mollusca embraces animals which have 

 the body soft and enveloped in a muscular skin, and in 

 most cases protected by a shell. They have a distinct 

 nervous system, consisting of ganglia, some of which sur- 

 round the oesophagus, and others, connected by nervous 

 filaments, are scattered throughout the body ; and they 



Fig. 371. 



Gasteropod. 



are furnished with organs more or less developed appro- 

 priate to the five senses of higher animals, and with 

 organs by which food is secured and digested, a heart 



