140 THE MECHANICAL FUNCTIONS. 



§ 3. Polypifera. 



The next step in the organic series introduces ns 

 to the extensive family of Polypifera. The transi- 

 tion from the structure of the sponge to that of the 

 polypus may be thus conceived. Suppose the ab- 

 sorbing orifices of the former to be enlarged, and 

 their number to be at the same time reduced : and 

 let these orifices be drawn out into tubes, and pro- 

 vided with vibratory cilia ; in addition to which, let 

 there be placed around their margin a circular row 

 of larger filaments, extremely flexible, and capable 

 of twining round any object that comes within 

 their reach, and of conveying it to the central ori- 

 fice, which performs the office of a mouth. Each 

 tube, thus furnished with a circle of radiating fila- 

 ments, or lentacula, as they are called, is deno- 

 minated a Polype* The animal structure thus 

 composed has received the name of Lobularia (Fig. 

 56), and is the genus among this tribe that ap- 

 proaches the nearest in its character to the sponge, 

 which it resembles in the nature of its internal 

 texture. Each of the polypes with which its sur- 

 face is studded has eight serrated tentacula. Fig. 

 57 represents one of these polypes detached. Po- 

 lypes may thus be united in immense numbers into 

 one mass, having mutual organic connexion. In 



* For the sake of greater distinctness I shall employ the term 

 polype to denote the single tube with its tentacula ; and shall desig- 

 nate by the Latin term polypus the entire animal mass composed of 

 an aggregation of these polypes. Polypifera, the name of the 

 order, expresses animals bearing polypes. 



