238 



rffYLUM ANNELIDA. 



duels. The posterior region of the body often forms a stalk by which 

 the shell is moored, but in many this stalk is absent, and the animal is 

 directly attached to the substratum. The sexes are sometimes separate, 

 but perhaps some are hermaphrodite. There is a metamorphosis in the 

 development, and the larva; resemble those of Polyzoa. Of the details 

 little is yet known. 



TESTICARDINES. 



The valves are hinged. 

 There is no anus. 

 Tercbratitla.. \Valdheiinia. 



ECARDINES. 



There is no hinge. 

 There is an anus. 

 Crania. 



Lingula, persistent since Palaeozoic 

 ages. 



