INFUSORIAL ANIMALCULES. 



19 



distinguished from each other by their structure: viz., the Polygastrica* or 

 many stomached animalcule, and the Rotatoriaf or wheel-animalcule. Other micro- 

 scopists, however, prefer to substitute the term Infusorial animalcules for the 

 Polygastrica. 



POLYGASTRIOA. If an animalcule of this class is viewed by the microscope, a 

 number of round spots within its body will be readily detected, which are often 

 quite large compared with the size of the living atom. These spots are so many 

 stomachs, connected together by a single tube, and forming the digestive apparatus 

 of the creature. If the water around the animalcule is clear, the stomachs will 

 appear more transparent than the rest of the body; but if it is tinted with sap- 

 green or carmine (which substances are usually employed) they will be seen more 

 distinctly; for the animalcule readily imbibes the colored fluid, and the stomachs 

 from their transparency then appear of the same hue as the liquid; while the tint 

 of the more solid portions of the body remains unchanged. The number of stom- 

 achs varies in different species. 



In the annexed cut a highly magnified view of a bell-shaped animalcule is pre- 

 sented, in which the stomachs and coronets of cilia are distinctly exhibited. 



None of this class of infusoria are more than the twelfth of an inch long, and 

 the smallest species, when full grown, do not exceed in extent the thirty-six 



Figure 6. 



thousandth 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. 



According to Ehrenberg the Polygastrica form a 

 very extensive division of the Infusoria ; but the inves- 

 tigations of later microscopists have shown that a large 

 number of classes of organisms, which Ehrenberg re- 

 garded as true animals, are simply vegetable structures, 

 as will be more fully explained in the following pages. 

 The number of species of the true Polygastrica is 

 therefore much less than it was formerly supposed to 

 be, and, consequently, the forms and conditions of life 

 at first assigned to them are now only partially true. 



Some of the Polygastrica are loricated, and others 

 illoricated. The shells are differently formed. In one 

 kind it consists of small rings between which cilia are situated, and in another the 

 lorica has the form of a shield. 



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

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

 eMia 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 

 their body, while in the Polygastrica they are distributed over the entire surface. 

 In some species the crowns of cilia consist of a single set, and in others several 



A BELL-SHAPED ANIMALCULE. 

 c. Cilia, s. The stomachs. 



* From the Greek polus, many, and gaster, a stomach, f From the Latin rota, a wheel. 



