SUB-KINGDOM III. ANNULOSA. 

 CLASS I. TUEBELLAKIA. 



THIS small Class of animals has usually been 

 confounded with the Worms (ANNELIDA), into 

 which indeed they merge by insensible gradations. 

 They may, however, at once be distinguished by 

 the surface of the body being entirely clothed with 

 vibratile cilia, the currents produced by which 

 may be distinctly seen by a comparatively low 

 microscopic power, though it requires high powers 

 to discern the cilia themselves. The substance of 

 their bodies is of a loose cellular character, slightly 

 consistent, and easily torn, in which the viscera 

 are excavated. In many of the genera the form 

 is exceedingly thin and flat, moving by an even 

 gliding action over solid bodies, like the Gasteropod 

 Mollusca, or swimming by means of a rapid undu- 

 lation of their thin margins; but in others the 

 body is more nearly cylindrical, and lengthened, 

 sometimes to an excessive degree; and in these 

 there are traces of that division into rings or 

 segments which we see carried to perfection in the 

 ANNELIDA. 



The organization of the TURBELLARIA is very 



