1 84 



MANUAL OF ZOOLOGY 



tent 



SECT. 



tent 



FIG. 103. Pedicellina. Showing successive stages (numbered / to 6) in the 

 development of zooids by budding, an, anus; gang, ganglion; mo, mouth; 

 tent, tentacles (retracted). (After Hatschek.) 



3. THE BRACHIOPODA 



The Brachiopoda, or Lamp-shells, are a group of marine animals 

 which present certain important features of resemblance to the Polyzoa, 

 and on that account are placed with them in a special phylum to which 

 the name Molluscoida is applied. The Brachiopoda are solitary, 

 never giving rise to colonies like those of the Polyzoa, and one of their 

 most striking characteristics is the possession of a calcareous shell which 

 bears a remarkable resemblance to that of the members of a widely 

 different group, the Pelecypoda of the phylum Mollusca, the group to 

 which the mussels, oysters, and clams belong. The shell (Fig. 104) 

 consists of two pieces or valves, one dorsal (d. v), the other ventral 

 (v. v), and the animal is attached by a horny stalk or peduncle (Fig. 

 ic>5,/</) which passes through an aperture (Fig. 104 f) in a process, 

 the beak (3), of the ventral valve. In the natural state the peduncle is 

 attached to a rock or other support, and the animal lies with the ventral 

 valve uppermost and the two valves gaping slightly. The end of the 

 valve at which the peduncle is situated is regarded as posterior, the 



