CLASSIFICATION OF POLYZOA. 581 



examination of anything more than the tentacular crown and the 

 oesophagus which it surmounts ; the stomach and the remainder of 

 the visceral apparatus being always retained within the cell. It 

 furnishes, however, a most beautiful object for the Binocular 

 Microscope, when mounted with all its Polypides expanded, in the 

 manner described in § 419. — Several of the Fresh-water Polyzoa 

 are peculiarly interesting subjects for Microscopic examination ; 

 alike on account of the remarkable distinctness with which the 

 various parts of their organization may be seen, and the very 

 beautiful manner in which their ciliated tentacula are arranged 

 upon a deeply-crescentic or horseshoe-shaped Lophophore. By this 

 peculiarity the Fresh-water Polyzoa are separated as a distinct Sub- 

 Class from the Marine ; the former being designated as Hippo- 

 crepia (horseshoe-like), while the latter are termed Infundibulata 

 (funnel-like). 



450. The Infundibulata or Marine Polyzoa, constituting by far 

 the most numerous division of the class, are divided into four 

 orders, as follows : — I. Cheilostomata, in which the mouth of the 

 cell is sub-terminal, or not quite at its extremity (Fig. 300), is some- 

 what crescentic in form, and is furnished with a movable (gene- 

 rally membranous) lip, which closes it when the animal retreats. 

 This includes a large part of the species that most abound on our 

 own coasts, notwithstanding their wide differences in form and 

 habit. Thus the Polyzoaries of some (as Flustra) are horny and 

 flexible, whilst those of others (as Eschara and Rdepora) are so 

 penetrated with calcareous matter as to be quite rigid ; some grow 

 as independent Plant-like structures (as Buyida and Gemellaria), 

 whilst others, having a like arborescent form, creep over the sur- 

 faces of rocks or stones (as Hippothoa); and others, again, have 

 their cells in close apposition, and form crusts which possess no 

 definite figure (as is the case with Lepralia and Membranipora). 

 — ii. The second order, Cyclostomata, consists of those Polyzoa 

 which have the mouth at the termination of tubular Calcareous 

 cells, without any movable appendage or lip (Fig. 301 ). This includes 

 a comparatively small number of genera, of which Crista and Tubu- 

 lipora contain the largest proportion of the species that occur on 

 our own coasts. — in. The distinguishing character of the third 

 order, Ctenosomaia, is derived from the presence of a Comb-like 

 circular fringe of bristles, connected by a delicate membrane, 

 around the mouth of the cell, when the animal is projected from 

 it ; this fringe being drawn-in when the animal is retracted. The 

 Polyzoaries of this group are very various in character, the cells 

 being sometimes horny and separate (as in Laguneula and Bower- 

 bankia), sometimes fleshy and coalescent (as in Halodactylus). — 

 iv. In the fourth order, Pedicellinece, which includes only a single 

 genus, Pedicellina, the Lophophore is produced upwards on the 

 back of the tentacles, uniting them at their base in a sort of 

 muscular Calyx, and giving to the animal when expanded somewhat 



