188 ZOOLOGY. 



CLASS IV. POLYZOA. 



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

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

 gestive tract flexed, the anus situated near the mouth. T/ie body usually 

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

 Tlie mouth surrounded by 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. Tlie embryo passing through a 

 morula, gastrula and trocJiosphere stage, the corm 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, Myriozoum.) 



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 Y. BRACHIOPODA (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 

 Sabella-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 Bracldopoda 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- 

 Iratulina 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 is 



