POLYGASTRIC ANIMALCULES; THEIR MOVEMENTS. 545 



aud swallowing entire the bodies of the Animalcules not very dis- 

 similar to themselves, to receive which the entrance to the 

 digestive cavity has to undergo a distention, that very much 

 alters their general form. In one genus, Nassula, there is a 

 very curious dental apparatus, for the prehension and reduction 

 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 contracts 

 by the approximation of these curious teeth ; these, although 

 flexible, appear to possess considerable firmness. 



1121. It is to the cilia, also, that the movements of the 

 greater part of the Animalcules, which freely swim through the 

 water, appear due. These movements are extremely various in 

 their character in different species ; and when a number of dis- 

 similar forms are assembled in one drop of water, the spectacle 

 is most entertaining. Some propel themselves directly for- 

 wards, with a velocity which appears (when thus highly magni- 

 fied) 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 an uniform series of gentle undulations or vibra- 

 tions; whilst others seem to perform consecutive leaps, of no 

 small extent compared with the size of their bodies. In short, 

 there is no 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 

 bodies of many species, which are believed by Ehrenberg to be 

 eyes. This belief rests only upon an analogy which may very 



