Introduction to Animal Morphology. 225 



the cell mouth to be continuous with the outer mem- 

 branous investment of the tentacles. It consists of a 

 layer of large, irregular, connective cells with (distally) 

 or without (proximally) a nucleated intercellular sub- 

 stance. Within is a layer of fine longitudinal and 

 transverse fibres, crossing each other at right angles, 

 and permeated by fine, netted canals containing oval 

 corpuscles. Each polypide or persona is lodged in a 

 cell, and possesses a crown of 8-80 ciliated, hollow, oval 

 tentacles* (branchiules, va7i Bcneden) like those of 

 Chaetopoda, whose cavities communicate with the 

 coeloma ; each tentacle consists of an outer wall of 

 round, often nucleated, cells, and an inner structure- 

 less layer. They are seated on a basis or lophopJwrey 

 either horseshoe-shaped, as in all the freshwater 

 genera, except Paludicella and Urnaria, or else cir- 

 cular, as in all the marine forms except Pedicellina 

 and Rhabdopleura. The former group have a buccal 

 shield, valve or epistome (homologous with the foot of 

 a Mollusc) arching over the mouth, and the tentacles 

 are often united for \-\ of their extent by a basal 

 membrane forming a calyx. The epistome is not to 

 be confounded with the operculum of the cell, an ecto- 

 cystic process found in Myriozoon and Chilostomum. 



Three kinds of appendages (undeveloped persons) are 

 found on the ectocyst of the colonies: — i. Avicularia — two- 

 armed graspers, with a calcareous basal part, in shape some- 

 what like a bird's head, with a horny, sometimes serrated, 

 beak, and a movable limb or under jaw ; between these there 

 is often a ciliated lobe. They are placed near the mouth, 

 and open and shut rhythmically, grasping prey. Three forms 

 are described — a. pedunculata, on a movable, often jointed, 

 stalk ; a. sessiHa, with no stalk ; a. immersa, sunk into a pit 



* Often in multiples of four. 



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