INFUSORIAT. ANIMALCULES. 61 



"The external organs of motion are flagelliforni filaments, 

 or vibratile cilii, or cirri^ more or less voluminous, or fleshy 

 prolongations, which (except those which are more or less 

 consistent) appeared formed of the same living substance, 

 and are contractile themselves, throughout the whole of 

 their extent. None are dermoid or corneaceous, nor 

 secreted by a bulb, except some siliceous or horny capsule 

 or shells, and the bundles of horny spiculi which invest 

 the mouth of certain species. All portions of the Infusoria 

 decompose almost immediately in water, after the death of 

 the animal. 



" The eggs of the Infusoria, their generative organs, their 

 organs of sense, their nerves and vessels, cannot be exactly 

 determined, and every thing inclines one to believe that 

 these animalcules, although endowed with a degree of 

 organization, in accordance with their mode of life, cannot 

 possess the same systems of organs as do the superior 

 animals." 



Having presented the reader with the opponents' ow^n 

 arguments to the classification I have adopted, I shall pro- 

 ceed at once to take a general survey of this class, re- 

 marking that whatever be the fate of the Polygastrica 

 (and some portions are certainly objectionable), I am con- 

 vinced an arrangement is yet to be discovered that will 

 supersede it. 



The Polygastrica constitute a natural group of animals, 

 and are as satisfactorily distinguished as any other class. 

 Touching their dimensions, none exceed the 1-1 2th of 

 an inch in length, and some of the smaller species (be- 

 longing to the genera Monas, Bodo, Bacterium, and the 

 single individuals of the Vibrio,) even when full grown, are 



