INFUSORIAL ANIMALCULES. 19 



description, which are mainly used as organs for prehen- 

 sion. These are generally at the extremity of a certain 

 prolongation of the body, which may be designated a foot- 

 like member. To the inexperienced observer, this process 

 has generally been supposed to be the tail ; but, not being 

 placed dorsally, with respect to the discharging orifice, it 

 must be considered as occupying the position of the foot. 

 In these creatures, there is a large development also of 

 those parts of the body to which the rotatory organs 

 are attached; and, in the case where two only of these 

 organs are seen, a projection may be noticed on each side 

 of the anterior portion of the animalcule, such as to 

 have obtained for them the appellation of ears. For 

 example, see fig. 416. 



SECTION III. OftheEijes, or Visual Organs of Infusoria. 



Our knowledge of the existence of these organs is wholly 

 attributable to the invention of the achromatic microscope. 

 In F. O. Muller's work, which contains drawings of the 

 larger number of the animalcules, lately figured by 

 Dr. Ehrenberg, and several of them made with much 

 exactness, though on a very small scale, there is not one 

 of the Polygastrica given as possessing the visual organ, 

 and but one species of the Rotatoria, in which he consi- 

 dered the existence of it as established. By referring to 

 our engravings, however, it will be seen that nearly all the 

 Rotatoria have eyes, and that many of the genera of the 

 Polygastrica are also furnished with them. If no other 

 proof than this could be obtained, therefore, of the 



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