BOOK NINTH. 

 AC EP H ALA 



CLASSIFICATION. 



§ 170. 



The Acephala are principally characterized in having a headless body, 

 and a very large mantle, which so envelops the body, that there is a spa- 

 cious and more or less closed cavity in which the oral and anal orifices are 

 often entirely concealed. 



Their body is either wholly asymmetrical, or divided into a right and a 

 left side. In this last case, the organs, excepting the digestive canal, are 

 in pairs; and the two sides are perfectly symmetrical, or one is developed 

 at the expense of the other. All Acephala are aquatic ; many are perma- 

 nently attached during life ; others creep about, and a few only can swim 

 freely. Copulatory organs are wanting throughout. 



ORDER I. TUNICATA. 



Body wholly asymmetrical and so enclosed in the mantle, that there are 

 only two narrow openings. 



Family: Ascidiae. 



Genera : A. Compositae. 



Didemnum, Diazona, Aplidmm, Botnjllus, Botrylloides, Leptodinum, 

 Eucoelium, Synoecium, Polycliniim, Sigillina, Perophora, Pyrosoma. 

 B. Simplices. 



Clavelina, Phallusia, Rhopalaea, Boltenia, Cynthia, Chelyosoma. 



Family : Salpinae. 

 Genus : Scdpa. 



ORDER II. BRACHIOPODA. 



Animals which are symmetrical and bivalved, and whose widely-open 

 mantle encloses two fringed, arm-like, protractile tentacles. 



