122 



THE MECHANICAL FUNCTIONS. 



by the Gulf stream, from the shores of the east to corre- 

 sponding latitudes of the new world. 



§ 3. Polypifera, 



The next step in the organic series introduces us to the 

 extensive family of Polypifera. The transition from the 

 structure of the sponge to that of the polypus may be thus 

 conceived. Suppose the absorbing orifices of the former to 

 be enlarged, and their number to be at the same time re- 

 duced: and let these orifices be drawn out into tubes, and 

 provided 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 orifice, which performs the office of a mouth. 

 Each tube, thus furnished with a circle of radiating fila- 

 ments, or tentacula, as they are called, is denominated a 

 Polype.^' The animal structure thus composed has received 

 the name of Lobularia (Fig. 5Q,) and is the genus among 



• For the sake of greater distinctness I shall employ the term polype to 

 denote the sing-le tube with its tentacula; and shall designate by the Latin 

 term polypus the entire animal mass composed of an aggregation of these 

 polypes. rolypiferUy the name of the order, expresses animals bearing po- 

 lypes. 



