8a THE VITAL FUNCTIONS. 



highly developed structure with respect to many 

 systems of organs, which we should never have 

 expected to meet with in animals situated so low in 

 the scale. As connected with the nutritive func- 

 tions, it may here be mentioned that the head of 

 this animalcule is provided with a regular appa- 

 ratus for mastication, consisting of serrated jaws; 

 each having from two to six teeth. These jaws are 

 seen actively opening and shutting when the animal 

 is taking its food, which consists of particles brought 

 within reach of the mouth by means of currents 

 excited by the motions of the cilia. 



Such are the simple forms assumed by the organs 

 of assimilation among the lowest orders of the ani- 

 mal creation ; namely, digesting cavities, whence 

 proceed various canals, which form a system for 

 the transmission of the prepared nourishment to 

 different parts; but all these cavities and canals 

 being simply hollowed out of the solid substance of 

 the body. As we ascend a step higher in the scale, 

 we find that the stomach and intestinal tube, to- 

 gether with their appendages, are distinct organs, 

 formed by membranes and coats proper to each ; 

 and that they are themselves contained in an outer 

 cavity, which surrounds them, and which receives 

 and collects the nutritious juices after their elabo- 

 ration in these organs. The Actinia, or Sea Ane 

 mone, for example, resembles a polypus in its gene- 

 ral form, having a mouth, which is surrounded with 

 tentacula, and which leads into a capacious stomach, 

 or sac, open below, and occupying the greater part 

 of the bulk of the animal ; but while, in the Po- 

 lypus, the sides of the stomach constitute also 

 those of the body, the whole being one simple sac ; 



