188 ZOOLOGY. 



Class IV.— POLYZOA. 



Ammals usuaUy forming moas-Uke or coraZ-like caZeareous or ehitiruni* 

 masses caUed corns, each, cell containing a worm-like animal, with the di- 

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

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

 Tlie mouth surroundedby a crown of long tentacles. Xo heart or vascular 

 system. Nervous system consisting of a single or douile ganglion situated' 

 between the Tnouih and ve^it, with nerves proceeding from it. Hermaphro- 

 ditic ; 'multiplying by budding or eggs. Tlie errAi-yo passing throxigh a 

 morula, gastrula and trocJtosphere stage, tlie corm being formed by iJia 

 budding of numerous ceUsfrom a primitive one. 



Orderl. Entoprocta. — Vent within tlie lopliophore. (Loxosoma.) 



Order 3. Ectoprocta. — Vent without the lophophore. (Lepralia, Es- 

 chara, Idmonea, Myriozoum.) 



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

 must he studied while aliTe 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. — Bkachiopoda {Lamp Shells). 



General Characters of Brachiopods.— This group is named 

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

 coiled up within tlie shell, and whicli correspond to the 

 lophophore of the Polyzoa and the crown of tentacles of the 

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

 a true, bivalved, solid shell, though it is usually inequivalTe, 

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

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

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

 synthetic type of worms, with some superficial molluscarL 

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

 bratulina septentrionalis, which lives attached to rocks in 

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

 shape somewhat like an ancient Eoman 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 



