OF ANIMALCULES. 105 



181. Cercaria turho. Tlie restless Cercaria, — This 

 species is shewn at figure 104 : the body is slightly con- 

 tracted near the middle, and is filled with spherical sacs ; 

 small eye-like dots may be observed, also, near the ante- 

 rior 5 the tail is setaceous. Found among duck- weed on 

 the surface of clear water. Length of body, in some spe- 

 cimens which I procured in December among confervas, 

 l-400th of an inch. 



182. Cercaria podura {Ichthydium poduray E.) The 

 podura Cercaria, — This animalcule belongs to the first 

 genus of the Rotatoria ; it produces a slight whirl in the 

 water, and forms a very good test of the excellency of a 

 microscope, a row of cilia being just discernible 

 with careful management. Its general appearance, 

 under an ordinary magnifier, is shewn at figure 114. 

 The body is spindle-shaped, the head obtusely rounded, 

 and the tail forked. It is transparent about the extre- 

 mities, and sometimes fine cilia may be discerned on 

 either side of the body : in its interior may be seen the 

 peristaltic action of the alimentary canal. In progress- 

 ing, it slowly revolves, the setaceous tail sometimes ap- 

 pearing single. It is found at the close of the year in 

 marshes, among lemna. 



183. Ci£RCAR\Aviridis{Eugle7iaviridis,E.) The green 

 Cercaria. — This is a highly-interesting creature : the 

 bright green colour of its body j its diaphanous extremi- 

 ties ; its well-defined orange-brown eye; and the nu- 

 merous transformations of its form, render it a very 

 entertaining object for the microscope ; in addition to 



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