CLASSIFICATION. 



and then the young are born alive. In all cases they possess at 

 birth nearly the form they preserve through life, and do not un- 

 dergo metamorphosis. 



We have already stated that mollusks differ very much in the 

 general form of their body, and as these external modifications 

 are accompanied by corresponding differences in the degree of 

 complication of their internal organization, they enable us to di- 

 vide these animals into six natural groups. The following table 

 will give an idea of this classification : 



(CLASSES.) 



in the form of an open sack in front, from i 

 which the head appears, surrounded by > CEPHALOPODA. 

 tentacula (Fig. 7, Page 19). } 



unprovided with ) 



arms and special > TUNICATA. 



organs of motion. " j 



Cuvier, and many other zoologists, arrange the cirrhopoda also 

 in the branch of mollusca ; but it is now ascertained that these 

 animals belong to the branch of articulata, the third great divi 

 sion of the animal kingdom. 



16 Into how many classes is the branch of mollus'ca divided ? 



