286 MANUAL OF ZOOLOGY. 



cells of the marginal ring, or "annulus," being spongy and 

 fiUed with air. They must be looked upon as "gemmce pecu 

 liarly encysted, and destined to remain for a period in a qui- 

 escent or pupa-like state." — (AUman.) 



As regards the development of the Polyzoa, the embryo 

 upon its emergence from the ovum presents itself as a ciliated, 

 free-swimming, sac-like body, from which the polypide is sub- 

 sequently produced by a process of gemmation. In the sin- 

 gular Rhabdopleura the primitive bud is enclosed between two 

 fleshy lobes or valve-like plates, attached along their dorsal 

 margin, and giving exit in front to the rudimentary lophophore. 

 As the development proceeds, these plates cease to keep pace 

 in their growth with the rest of the bud ; till ultimately they 

 appear as a peculiar shield-like organ on the hsemal side of the 

 lophophore. These lobes have been compared by Dr Allman 

 with the mantle-lobes of the Lamellibranchiata. 



Divisions of the Polyzoa. — The Polyzoa are divided into 

 two divisions or orders— -tlfe Phylactolamata (fig. 102, 3), dis- 

 tinguished by the possession of a bilateral horse-shoe-shaped 

 lophophore, and of an " epistome " arching over the mouth ; 

 and the Gymnolmmaia (fig. 102, 2), in which the lophophore 'is 

 orbicular, and there is no epistome. 



Table of the Divisions of the Polyzoa. 



Order I. Phylactol^mata. 



Lophophore bilateral ; mouth with an epistome. 

 Sub-order I. Lophopea (fresh-water). 



Arms of lophophore free or obsolete ; consistence homy, sub-cal- 

 careous. 

 Sub-order 2. Pedicellinea (marine). 



Arms of lophophore united at their extremities ; consistence soft, 

 fleshy. 

 Sub-order 3. Rhabdopleurea (marine). 



Coenpecium branched, adherent, membranous, with a solid chiti- 

 nous rod on its adherent side, to which the polypites are attached 

 by their. funiculi. Lophophore completely hippocrepian, with a 

 peculiar shield-like body on its haemal side. No epistome (?) 



Drdrr II. Gymnol^mata. 



Lophophore orbicular, or nearly so ; no epistome. 

 Sub-order 4. Paludicellea (fresh-water). 



Polypide completely retractile ; evagination of tentacular sheath 

 imperfect ; consistence homy or sub-calcareous. 

 Sub-order 5. Cheilostomata (marine). 



Polypide completely retractile ; evagination perfect ; orifice of cell 

 sub-terminal, of less diameter than the cell, and usually closed with 

 a movable Kp or shutter, sometimes by a contractile sphincter; cells 

 not tubular; consistence calcareous, homy, or fleshy. 



