THE DEVELOPMENT OF A MOLLUSK 51 



the animal withdraws into it. On the head are seen the two 

 eyes and near them the tentacles. 



The veliger stage, though more or less suppressed in land 

 mollusks, is common to all gastropods. By an additional series of 

 changes, consisting in a continued growth and development in 

 certain directions, this larva is ultimately metamorphosed into 

 the adult form of its species. 



MODEL 22 



A section of the veliger showing the internal anatomy. 

 [27] 



