WHEEL-BEARING ANIMALCULES. 181 



the real tooth, while the other serves as a jaw. 

 These three portions work with their inner edge 

 upon the facets of the central piece, and this edge 

 appears to be jagged or serrated, the better to tear 

 the substances on which it acts. Minute as are 

 these curious organs, the transparency of the 

 rotifera permits them to be distinctly seen, under 

 a powerful microscope, which also demonstrates 

 their effects upon the bodies of the smaller animal- 

 cules on which the various species prey ; for, as 

 with fishes, they are the food of each other, and 

 the warfare is perpetually carried on. The hard- 

 ness of these teeth is not a little surprising ; they 

 may be detached from the body of the animalcule in 

 a perfect condition, and be submitted by themselves 

 to examination beneath a microscope ; they vary 

 in minor particulars, as form and size, in every 

 species ; but their essential characters appear to be 

 the same in all. 



From this teeth -furnished gizzard, or preparatory 

 receptacle, a passage, varying in length in different 

 animalcules, leads to the true stomach, or digesting 

 cavity, to which the food, after being subdivided, 

 is conveyed. The form and the relative capacity 

 of the stomach, like those of the gizzard, are very 

 variable ; but in all these rotiferous animalcules 

 this part is furnished with certain appendages, 

 which are regarded as being of a glandular struc- 

 ture, and destined to secrete a fluid essential to 

 the performance of digestion. 



