12 NATURAL HISTORY 



research into those recondite truths which may lead not 

 merely to the gratification of our curiosity but to some 

 of the most important and scientific results. 



For a lapse of years, after the publication of Miiller's 

 " Animalia Infusoria," in 1786, this branch of Natural 

 History remained stationary, if not utterly disregarded ; 

 nor, indeed, did it, until very recently, assume what may be 

 termed a regular form, constructed of materials the most 

 precious of all, viz. truths brought together by practical 

 and diligent investigation. To Dr. Ehrenberg's late ob- 

 servations, although they apply to such only as belong 

 strictly to the Phytozoa*, we are greatly indebted. La- 

 marck, too, in 1815, and Cuvier, in 1817, made consider- 

 able advances in classification : but then, as the systems 

 of these two last-mentioned Naturalists were not founded 

 upon a rigid inspection of the Animalcules themselves, 

 I have deemed it advisable, in the general arrangement 

 of this little Treatise, to abide by those of Miiller and 

 Ehrenberg. 



The term Animalcule, which implies nothing more 

 than the diminutive of animal, has been commonly used 

 to denote those living creatures inhabiting fluids, which 

 are too minute to be scanned, or even seen by the naked 

 eye : such, for instance, as those produced in incon- 

 ceivable numbers from infusions of animal and vege- 

 table mater : it comprehends as well such as are found 

 in, and are peculiar to, the bodies of larger animals : 



* Book III. 



