500 



ZOOLOGY. 



construct as dwellings a long tube, formed either of calcareous 

 matters secreted by the skin (Fig. 528), or consisting of 

 sand and fragments of shells, agglutinated by means of a 

 gelatinous substance ; several, as the arenicola, plunge deeply 

 in the sand (Fig. 56); others conceal themselves under stones ; 

 finally, there are annelides, as the leech, which live in fresh 

 waters : so also does the nais, which more resembles the earth- 

 worm ; and these last, called by zoologists lumbrici, are land 

 animaLs. 



CLASS OF THE KOTIFERA. 



586. These beings, which have been often confounded with 

 the infusoria, are nevertheless quite distinct. Their structure 

 is very complex, and we owe the discovery of this fact to the 

 microscope, and to the profound researches of M. Ehrenberg, 

 of Berlin. Before his time they were thought to be animals 



Fig. 529. The Hydatina.* 



* Anatomy of the Hydatina, a microscopic animalcule next the Botifera : 

 a, vibratile cilia ; b, fleshy mass surrounding the mouth and moving the 

 j aws ; c, the stomach ; d, the cloaca ; e, the anus ; f, salivary glands ; g, 

 ovaria ; h, the muscles. 



