426 TEXT-BOOK OF ZOOLOGY 



ingly formerly classed with the latter, there being a further popular 

 superstition that they gave origin to ducks — whence in Germany the 

 name for Barnacles (Lepas) is duck mussel (Entenmuschel). It is 

 only a study of their development that has revealed these animals to 

 be crustaceans. Their larvse were, in fact, found to be free-swimming 

 organisms, resembling in all respects the larvae of other crustaceans. Only 

 after several metamorphoses they become fixed to some solid object, and 

 assume the shape and form of the barnacle. By means of delicate 

 tendril-like appendages called cirri, which may be seen protruding from 

 a cleft in the shell, these animals sweep a constant current of water 

 laden with food into their interior. , 



To this order also belong the unstalked or sessile Acorn Shells 

 (Balanus), which may be seen at low water, looking like small warts, 

 fixed to rocks, shells of molluscs, etc. (see illustration, p. 421). 



