158 MARVELS OF POND-IJFE. 



of the moll u sea. The lolyzna are chiefly ma- 

 rine, and the common ''sea-mat," often erroneously 

 treated as a sea-ioeed^ is a well-known form. Another 

 species often picked up on our coasts is the Ser- 

 tulaina, or Sea-Fir, composed of delicate branching 

 stems of a horny-looking substance, which, under 

 a pocket-lens, is found to contain an immense 

 number of small cells iiduibited by the Polyzoa. 



These animals w^ere formerly associated with the 

 polyps, to which they bear a strong superficial re- 

 semblance; but they are of a much higher degree 

 of organization, as will be seen by comparing what 

 has been said in a former chapter on the Hydra., 

 with the description which we now proceed to 

 abridge from Dr. Allman's splendid monograph on 

 the fresh-w^ater kinds. In order to get a general 

 conception of a Polyzoon, the Professor tells us to 

 imagine an alimentary canal, consisting of aesopha- 

 gus, stomach, and intestine, to be furnished at its 

 origin with long ciliated tentacles, and to have a 

 single nervous ganglion on one side of the Eesophngus. 

 We must then conceive the intestine bent back till 

 its anal orifice comes near the mouth ; and this 

 curved digestive tube to be suspended in a bag con- 

 taining fluid, and having two openings, one for the 

 mouth and the other for the vent. A system of 

 muscles enables the alimeutai'v tube to be retracted 

 or protruded, the former process pulling the bag 



