INFUSORIA. 



23 



is forming in some other part ; one portion is contracting, 

 another enlarging ; so that the only idea that can be 

 given of its shape, is by comparing it to the figure of a 

 country upon a map, which is perpetually transformed 

 into that of some other country. 



These are but a few examples of the variety of form 

 which this curious class of animals presents to us : it re- 

 mains now only to give, to those who may be desirous of 

 examining them for themselves, a few instructions to aid 

 their researches. A good microscope is, of course, indis- 

 pensable ; if the study is intended to be pursued scienti- 

 fically, a compound achromatic, with magnifying powers 

 ranging from fifty to five hundred diameters, must be 

 employed ; but very much entertainment, and a good 

 idea of many of the forms, may be obtained with an 

 ordinary simple microscope of three powers. The pene- 

 trating and defining properties of a microscope are of more 

 importance than mere enlargement, 



If we were asked where specimens are to be obtained, 

 we might reply, almost everywhere, provided water be 

 present : but even in the air they have been lately 

 detected by the eminent Prussian professor. In ditches 

 and ponds, in the trenches of meadows, in the ruts of 

 highroads, in marshes, in lakes and rivers, in estuaries, and 

 even in the sea, various species may at almost all times be 

 found. Stagnant waters, especially such as are covered 

 with a thick scum, contain some species in immense 

 abundance, but these are generally of the simplest struc- 

 ture : little hollows in boggy ground, especially where a 

 red sediment betokens the presence of oxide of iron, fre- 

 quently contain species of great rarity and beauty ; but 



