THE BBACHIOPODS. 
57 
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 
larvae 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. Q2.—Lingula pyramidafa with its sand-tube; natural size. 
Polyzoa 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 known. One living 
species of Lingula (Fig. 62) 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. 
Literature. 
A. Hancock. On the Organization of the Brachiopoda. Phil. 
Trans. 1858. 
E. 8. Morse. On the Systematic Position of the Brachiopoda. 
Proc. Boston Soc. Nat. Hist., xv. 1873. 
With the essays of Brooks, Lacaze-Duthiers, Kowalevsky, Ball, 
etc. 
