50 7 HE AMERICAN MUSEUM JOURNAL 



mollusk larva is thus established and the definitive asymmetry 

 of the adult is foreshadowed. 



Models 21 and 22 show the completed larva, the free-swim- 



MODEL 21. SIDE VIEW 



The mollusk larva, or the veliger, completed. The velum, or swimming 

 organ, about the anterior end bears two rows of cilia. The foot is large and 

 prominent and bears on its under surface the lid, or operculum, by which the 

 opening of the shell is closed when the animal withdraws into it. On the head 

 are seen the two eyes. The two raised points near these mark the position of 

 the feelers or tentacles. 



ming veliger with its fully formed ciliated velum, or swimming 

 organ, the shell and the large foot, bearing on its lower surface 

 the operculum, or lid, by means of which the shell is closed when 



[26J 



