INFUSOKIAL ANIMALCULES; THEIR MOVEMENTS. 549 



lion of the cilia which surround it ; in this manner a vortex is 

 produced in the fluid, which brings the particles floating in it, 

 or other Animalcules swimming in its neighbourhood, within the 

 grasp of the lips of that aperture. In one genus, Nassula, there 

 is a very curious dental apparatus, for the prehension and re- 

 duction of food. This consists of a sort of cone, formed by a 

 large number of diverging flexible bristle-like organs, at the apex 

 of which the mouth is placed, whilst the base can be projected 

 and expanded so as to inclose the prey, over which it then con- 

 tracts by the approximation of these curious teeth ; these, al- 

 though flexible, appear to possess considerable firmness. 



1209. It is to the cilia, also, that the movements of the 

 greater part of the animalcules, which swim freely through the 

 water, appear to be due. These movements are extremely 

 various in their character in different species ; and when a 

 number of dissimilar forms are assembled in one drop of water, 

 the spectacle is most entertaining. Some propel themselves 

 directly forwards, with a velocity which appears (when thus 

 highly magnified) like that of an arrow, so that the eye can 

 scarcely follow their movement ; whilst others drag their bodies 

 slowly along, like the leech. Some make a fixed point of some 

 portion of the body, and revolve around it with great rapidity ; 

 whilst others scarcely present any appearance of animal motion. 

 Some move forwards by a uniform series of gentle undulations 

 or vibrations ; whilst others seem to perform consecutive leaps, 

 of no small extent compared with the size of their bodies. In 

 some instances the body is furnished with stiff bristles and hooks, 

 by the agency of which the Animalcule is enabled to run and 

 leap upon the stems and leaves of aquatic plants. In short, there 

 is scarcely any kind of movement, which is not practised by these 

 Animalcules. They have evidently* the power of steering clear 

 of obstacles in their course, and of avoiding each other when 

 swimming in close proximity. By what kind of sensibility the 

 wonderful precision and accuracy of their movements is guided, 

 is yet very doubtful. The general surface, in those whose 

 bodies are not inclosed in a firm envelope, appears very sus- 

 ceptible of impressions. No organs of special sensation, however, 

 can be detected; except certain red spots observable in the 



