TEE BBACHIOPODa. 47 



ciliated larva like that of the true worms, which after swim- 

 ming about finally becomes fixed by a stalk to rocks. 



While in their development the Brachiopods recall the 

 larvffi of the true worms, they resemble the adult worms in 

 the general arrangement of the arms and viscera, though 

 they lack the highly developed nervous system of the Anne- 

 lids, as well as a vascular system, while the body is not 

 jointed. On the other hand they are closely related to the 

 Polyzoa, and it seems probable that the Brachiopods and 



Fig. 50. — Lingulapyramidata with its sand-tube; natural size. 



Poh/zoa were derived from common low vermian ancestors, 

 while the true Annelids probably sprang independently 

 from a higher ancestry. They are also a generalized type, 

 having some molluscan features, such as a bivalved shell, 

 though having nothing homologous with the foot, the shell- 

 gland or odontophore of mollusks. 



The class of Brachiopods is a very ancient one, nearly 

 2000 species of fossil Brachiopods being knoT^m. One living 

 species of Lingula (Fig. 50) differs but slightly from the 

 most ancient fossil species. It lives buried in the sand, 

 where it forms a tube of sand around the stalk, just below 

 low-water mark, extending from Chesapeake Bay to Florida. 



LiTERATUKE. 



A. Hancock. On the Oigauizalion of the Bracliiopoda. Phil. 

 Trims. 1858. 



E. S. Morse. On llje Systematic Position of the Bracliiopoda. 

 Proc. Boston Soc. Nat. Hist., xv. 1873. 



With the essays of Bioolvs. Lacaze-Duthiers, Kowalevsky. Dall, 

 etc. 



