20 



VIEWS OF THE MICROSCOPIC WORLD. 



andth part of an inch. Uniting, however, in infinite 

 multitudes, the more minute kinds form various colored 

 'masses, several feet in length. The young of many 

 species are doubtless too minute to be visible even un- 

 der the highest powers of the microscope. 



Most of the Poly gas trica reside in fresh water, but 

 many species inhabit the ocean. They are likewise 

 found living in moist earth, in peat bogs, in animal 

 fluids, and in water in which astringent substances, such 

 as bark, have been infused. It has even been supposed 

 that from their extreme lightness some species may 

 dwell in the moisture of the atmosphere, being driven 

 about in unseen countless numbers, at the sport of every 



A BELL-SHAPBTD ANIMALCULE, wind. One-half of the kinds composing this class are 

 c. cilia, s. The stomachs, loricated, the other half illoricated; and from the 

 former are derived those vast collections of minute shells, which often con- 

 stitute for leagues a large portion of the surface of the earth ; the enduring me- 

 morials of innumerable beings which perished centuries ago. 



ROTATORIA. The second class of Infusoria have received the appellation of 

 Rotatoria, as has already been stated, from the circumstance that the circles of 

 cilia which surround the upper part of the body of the animal appear when in 

 motion to revolve like a wheel. The cilia are found upon no other portion of 



Figure 7. 



their body, while in the Poly- 

 gastrica they are distributed 

 over the entire surface. In some 

 species the crowns of cilia con- 

 sist of a single set, and in oth- 

 ers several circular rows of dif- 

 ferent forms are distinctly no- 

 ticed. This class of Infusoria is 

 endowed with a highly perfect- 

 ed organization, and on account 

 of their comparatively large 

 size, some of them attaining a 

 length of one-thirtieth of an 

 inch, both their external and 

 internal structure are well re- 

 vealed by the microscope. The 

 Rotatoria possess a single sto- 

 mach, and many kinds are 

 furnished with jaws and teeth, 



aa. The Cilia, bb. The Eyes. c. The Jaws and Teeth. wm ' ch toget}ier with other 



parts will be particularly described hereafter, when treating of individual ani- 



