THE POLYZOA. ZO 



VIII. THE POLYZOA. 



Notwithstanding the invariably minute size of the organisms 

 which constitute this class, they exhibit a very great advance in 

 complexity of structure. In such a compound Polyzoon as the 

 Sea-mat, or Flustra, the entire surface of the foliaceous expan- 

 sion, on being examined by the microscope, will be found to be 

 beset with an infinitude of minute apertures leading into little 

 chambers, out of each of which, when the animal was living and 

 active, multitudes of little creatures might be seen protruding the 

 oral extremities of their bodies. The ends of the branches of the 

 freshwater genus Plumatella, represented in Fig. 8, present a simi- 

 lar spectacle. Each mouth is surrounded by a circlet of tentacles ; 

 and, as every tentacle is fringed with long and active vibratile 

 cilia, lashing the water towards the mouth, hundreds and thou- 

 sands of little Maelstroms are created, each tending to suck down 

 such nutritious bodies, living or dead, as come within its range. 

 The mouth (Fig. 9) leads into a long and wide pharyngeal 

 and cesophageal tube, which opens, below, into a definite 

 stomach. From this is continued a distinct intestine, which 



Fig. 8. Plumatella repens, a fresh-water Polyzoon, magnified (after Allrnan). 



bends upon itself towards the oral end of the body, so as to form 

 a sharp angle, and then terminates upon the outer surface near 

 the mouth ; so that we have here, for the first time in our 

 ascending survey of the Animal Kingdom, an animal possessing 

 a complete intestine, not only structurally separated from the 



