TEE BBAOHIOPODS. 



45 



the commonest objects of the sea-shore. They are minute, 

 almost microscopic creatures, social, growing in communi- 

 ties of cells, forming patches ^\\ 

 on sea-weeds and stones (Fig. 

 46, Memhranipora solida). Cer- 

 tain deep-water species grow in 

 coral-like forms (Fig. 47, Myrio- 

 zoum subgracile), while the chit- 

 inous or horny Polyzoa are often 

 mistaken for sea-weeds on the 

 one hand, and Sertularian Hy- 

 droids on the other. 



The animals inhabiting the 

 microscopic cells are worm-like 

 creatures (Fig. 48), with the di- 

 gestive canal bent on itself and 

 ending near the mouth, the lat- 

 ter surrounded, as in the larger 

 fresh- water species (Fig. 48, hr), 

 with a horseshoe-shaped crown, 



or in the smaller marine forms F'o- <8.- qrganjzation^of a Poiy- 

 a circle of slender ciliated ten- 

 tacles. The fresh- water forms 

 {Phimatella, etc.) secrete no 

 solid shell, and are either moss- 

 like, or form large rounded 

 masses of a jelly-like substance.* 



zoon. A^Faliidictlla Ehrenbergii. 

 B, PUilflatella frutico.';a. 6r. ten- 

 tacular branchise of lophopliore; 

 x^ oesophagus; v, stomach; r, in- 

 testine: a, an\is; i, cell; x. poste- 

 rior, x^, anterior cord, at the in- 

 sertion of which into the body the 

 generative products are devel- 

 oped; f, testes; o, ovary; r*i, re- 

 tractor muscles of the anterior 

 portion of the cell ; nir, principal 

 retractor muscle. 



Class V. — Brachiopoda (Lamp Shells). 



General Characters of Brachiopods. — This group is named 

 Brachiopoda, from the feet-like arms, fringed with tenta- 

 cles, coiled up within the shell, and which correspond to 

 the horseshoe-shaped crown of the Polyzoa and the crown 

 of tentacles of the Sabella-like worms. From tlie fact that 

 the animal secretes a true bivalved, solid sliell, though it 

 is usually inequivalve, i.e., the valves of different sizes, the 



* See the works of Allman, Hinks, Smitt, Saknsky, Sais, etc, 



