188 ZOOLOGY. 



CLASS IV. POLYZOA. 



Animals usually forming moss-like or coral-like calcareous or chitinou 

 masses called corms, each cell containing a worm-like animal, with tlie di- 

 gestive tract flexed, the anus situated near the mouth. The body usually 

 drawn in and out of the cell by the action of retractor and adductor muscles. 

 The mouth surroundedby a crown of long tentacles. No heart or vascular 

 system. Nervous system consisting of a single or double ganglion situated 

 between the mouth and vent, with nerves proceeding from it. Hermaphro- 

 ditic ; multiplying by budding or eggs. The embryo passing through a 

 morula, gastrula and trochosphere stage, the conn being formed by the 

 budding of numerous cells from a primitive one. 



Order 1. Entoprocta. Vent within the lophophore. (Loxosoma.) 



Order 2. Ectoprocta. Vent without the lophophore. (Lepralia, Es- 

 chara, Idmonea, Myriozouin.) 



Laboratory Work. The Polyzoa are too small to dissect, and 

 must be studied while alive as transparent objects, and may be kept. 

 in aquaria. The corms in part or whole can be mounted for the mi- 

 croscope as opaque objects. 



CLASS V. BIIACHIOPODA (Lamp Shells). 



General Characters of Brachiopods. This group is named 

 Bracliiopoda from the feet-like arms, fringed with tentacles, 

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

 lophophore of the Polyzoa and the crown of tentacles of the- 

 Sahella-like worms. From the fact that the animal secretes- 

 a true, bivalved, solid shell, though it is usually inequivalve,. 

 i.e., the valves of different sizes, the BracMopoda were gener- 

 ally, and still are by some authors, considered to be mol- 

 lusks, though aberrant in type. They may be regarded as a 

 synthetic type of worms, with some superficial molluscan 

 features. The shell of our common northern species, Tere- 

 bratitlina septentrionalis, which lives attached to rocks in 

 from ten to fifty or more fathoms north of Cape Cod, is in 

 shape somewhat like an ancient Roman lamp, the upper and 

 larger valve being perforated at the base for the passage- 

 through it of a peduncle by which the animal is attached 

 to rocks. The shell is secreted by the skin (ectoderm), and i& 



