262 DESCRIPTION OF [Polygastrica. 



Figures 238 and 239 are two stalkless creatures; from 

 their different appearances in the latter state, Miiller has 

 described them not only as different species, but under 

 different genera. In Die Infusionsthierchen, there are 

 eighteen names under which that author has described 

 them. Length 1 -430th to l-24th ; stalk six times its 

 length. 



" This entertaining and well-known animalcule is usually 

 found attached to any extraneous body, as the leaves of 

 duck-weed, small aquatic shells, clusters of ova, and the 

 larvae of insects ; an example of the latter is shewn in the 

 Microscopic Illustrations, fig, 30, where it may be consi- 

 dered as a parasite, or rather an epiphytes. As they are, 

 when fully developed, attached mostly to some stationary 

 object, they afford many facilities to the microscopist for 

 his observation ; they form a good object also for ascer- 

 taining the defining power of his instrument, and his 

 expertness in its management, as much of the effect will 

 depend on the manner in which he directs the illumina- 

 tion. If this be not attended to, and the instrument has 

 not sufficient power and penetration, it will only exhibit 

 two cilii instead of a circular row ; indeed, this animalcule 

 is described and drawn in this manner, in the old authors, 

 an error which recent improvements in the microscope 

 have demonstrated. 



" When in search of prey they stretch out the stem, and 

 by means of a vibratory motion communicated to the cilii 

 they agitate the water, and occasion a current towards 

 them ; this brings along with it the small particles of 

 matter on which they feed. Should any circumstance 

 disturb the water, or a large animal approach them, they 



