414 THE AQUARIAN NATURALIST. 



betide the animalcule races cast by mischance within 

 the fatal circle ! 



The cause of the existence of this miniature Cha- 

 rybdis is to be looked for in the structure of the ten- 

 tacula, which, when examined with a good microscope, 

 are found to be armed at the back by about a dozen 

 fine hair-like processes, which project from them nearly 

 at right angles, while on either side they are richly 

 furnished with vibratile cilia in constant and rapid 

 motion, exhibiting a spectacle of extraordinary, we 

 might almost say, of matchless beauty. All particles 

 therefore which come within the reach of these ciliary 

 currents are transmitted along the surface of the 

 tentacles, until they are finally engulfed in the open 

 mouth, which gapes to receive them. 



Let the student, however, remember, that this 

 ciliary apparatus is to be recognized in general only 

 under favourable conditions, and by the aid of optical 

 instruments of superior power and quality, although 

 the effect produced may often be detected when the 

 cilia themselves are imperceptible. The discovery of 

 cilia upon the tentacula is, indeed, of very recent date ; 

 nevertheless, their presence forms the leading cha- 

 racter whereby the Polyzoa are distinguishable from 

 the Hydriform Zoophytes, and is invariably accom- 

 panied with an organization far more complicated 

 than that possessed by the unciliated Polyps. 



On examining the animal under the microscope, 

 when placed in water to which a little carmine has 

 been added, the movements of the streams of water 

 produced by the ciliary action can be more distinctly 

 observed. The two rows of cilia attached to each 



