CHORD ATA 339 



as Chordata, which includes also the backboned or verte- 

 Oh brate animals and certain less-familiar creatures. 



Chordate animals are coelomate Metazoa dis- 

 tinguished by the possession of a notochord, a hollow, 

 dorsal nerve cord, gill clefts, and almost always a muscular 

 hinder or " tail " region which contains no viscera and is 

 used, either for driving or steering, in locomotion. In 

 many members of the group, however, some or all of these 

 features may be present during development and lost by 

 the adult, as the adult frog has lost the notochord, gill 

 clefts, and tail which were possessed by the tadpole. 



