162 THE MICROSCOPE AND ITS REVELATIONS. 



Infundibulata (funnel-like). The cells of the Hippocrepia are for the most 

 part lodged in a sort of gelatinous substratum, which spreads over the 

 leaves of aquatic plants, sometimes forming masses of considerable size; 

 but in the very curious and beautiful Cristatella, the polyzoary is unat- 

 tached, so as to be capable of moving freely through the water. ' 



553. The Infundibulata or Marine Polyzoa, constituting by far the 

 most numerous division of the class, are divided into four Orders, as fol- 

 lows: i. Cheilostomata, in which the mouth of the cell is sub-terminal, 

 or not quite at its extremity (Fig. 380), is somewhat crescentic in form, 

 and is furnished with a movable (generally 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 F lustra) 

 are horny and flexible, whilst those of others (as EscJiara and Retepora) 

 are so penetrated with calcareous matter as to be quite rigid; some 

 grow as independent plant-like structures (as Bugula and Gemellaria), 

 whilst others, having a like arborescent form, creep over the surfaces 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}. n. 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. 381). This includes a comparatively small number of 

 genera, of which Crisia and Tubulipora contain the largest proportion 

 of the species that occur on our own coasts. in. The distinguishing 

 character of the third order, Ctenosomata, is derived from the presence 

 of a comb-like circular fringe of bristles, connected by a delicate mem- 

 brane, 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 Laguncula and Bowerbankia), 

 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 the form of an inverted bell, like that of 

 Vorticella (Fig. 305). As the Polyzoa altogether resemble Hydroid 

 Zoophytes in their habits, and are found in the same localities, it is not 

 requisite to add anything to what has already been said ( 521), respect- 

 ing the collection, examination, and mounting of this very interesting 

 class of objects. 2 



554. A large proportion of the Polyzoa of the first Order are 

 furnished with very peculiar motile appendages, which are of two kinds, 

 avicularia and vibracula. The avicular-ia or * bird's-head processes/ so 

 named from the striking resemblance they present to the head and jaws 

 of a bird (Fig. 381, B), are generally ' sessile ' upon the angles or 



1 See Prof. Allman's beautiful " Monograph on the British Fresh-water Poly- 

 zoa," published by the Ray Society, 1857. 



2 For a more detailed account of the Structure and Classification of the Marine 

 Polyzoa, see Prof. Van Beneden's ' Recherches sur les Bryozoaires de la Cote 

 d'Ostende,' in " Mem. de 1'Acad. Roy. de Bruxelles," torn, xvii.; Mr. G. Busk's 

 " Catalogue of the Marine Polyzoa in the Collection of the British Museum;" Mr. 

 Hincks's " British Marine Polyzoa," 1880; and Nitsthe, ' Beitrage zur Kenntniss 

 der Bryozoen, in Zeitschrift f. wiss. Zool.," Bde. xx., xxi., xxiv. 



