210 



ZOOLOGY. 



classes, the names of which we have already pointed out in 

 the preceding considerations. 



381. The primary division of the molluscous animals 

 presents organic modifications necessitating a similar subdivi- 



Shell.Mantle.Tentacula. Mouth. Nerves.Muscles. 



Foot. - 



Intestine. [~ 



Stomach. 



Branchiae. - 



Mantle. 



Anterior 

 Ganglions. 



Intestine. 



Posterior 

 Ganglions. 



Muscle. 



Anus. 



Respiratory Tubes. 

 Fig. 160. Anatomy of an Acephalous Mollusc (la Mactre : Mactra). 



sion. In the molluscs, properly so called, there is a nervous 

 system, composed of two or more pairs of nervous ganglions, 

 reunited by medullary cords (Fig. 156) ; and reproduction is 



