108 BRYOZOA. 



delicate and perfectly transparent tube of horny texture, which 

 arises from a repent stem, common to a great many individuals, 

 found aggregated in small patches upon the surface of Flustra 

 foliacea, upon which they are apparently parasitic. 



The mouth is surrounded by ten long and slender tentacula, 

 (Jig. 45,) which, during the expanded state of the animal, are 

 kept quite straight and motionless, as represented in the drawing. 

 Each tentacle is provided upon its outer aspect with a series 

 of stiff and immoveable spines, probably serving to keep off any 

 foreign bodies, which, by their proximity, might interfere with the 

 ciliary movements immediately to be described. 



Besides the stiff spines, the tentacula are covered with an im- 

 mense number of vibrating cilia, which at the will of the animal are 

 thrown into most rapid movement, so as to produce strong and 

 continuous currents in the surrounding fluid, by which particles 

 floating in the neighbourhood are hurried along with great velocity. 

 From the direction of the streams produced by the cilia, namely, 

 towards the mouth, we at once perceive the utility and beauty 

 of the contrivance which compensates to a great extent for the 

 fixed condition of the Bryozoon ; animalcules floating in the vi- 

 cinity no sooner come within the influence of the currents so pro- 

 duced, than they are forced towards the mouth, which is placed 

 at the roots of the tentacula, and, being at once seized, are imme- 

 diately swallowed. 



The tentacula themselves, notwithstanding their immobility dur- 

 ing the process of watching for prey, are highly irritable, and sensi- 

 ble of the slightest contact. No sooner does an animalcule im- 

 pinge upon any part of their surface, than the tentacle touched 

 bends with extraordinary quickness, as if endeavouring to strike it 

 towards the mouth ; and, if the object be sufficiently large to touch 

 several at the same moment, all the tentacula simultaneously co- 

 operate in seizing and retaining it. 



(146.) The existence of the cilia upon the tentacula would seem to 

 be characteristic of the BRYOZOA, and is invariably accompanied, as 

 far as our information extends at present, with a digestive apparatus 

 of far more complex structure than what we have seen in the un- 

 ciliated polyps, for in the class before us, besides the stomach, we 

 find a .distinct intestinal tube and anal outlet. In the specimen 

 under consideration the organization of the alimentary organs is 

 even rendered more elaborate than is usual in the class, from the 

 addition of a gizzard or cavity in which the food is mechanically 



