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O. F. MULLER, 1773-1786. 15ledge of the larger forms of animalcules, chiefly Vorticellidae and Stentoridae,preceding the appearance of what to the present day holds rank as theearliest standard work that embodies a complete and systematic account ofthe members of the infusorial world. Reference is here made to the'Animalcula Infusoria' of Otho Friedrich Miiller, a posthumous quartovolume published in the year 1786, containing no less than fifty plates and367 pages of letterpress devoted to the description and illustration of closeupon three hundred species, fluviatile and marine, investigated and drawnfrom the life by this indefatigable worker during a period extending overno less than twenty years.This early pioneer in the then terra incognita of the Protozoicsub-kingdom had already in his 'Vermium terrestrium et fluviatilium'succincta Historia,' Zoologica Danicae Prodromus,' and 'Zool. Dan. Icones,'published respectively in the years 1773, 1776, and 1779, given descriptionsand illustrations of a large number of these numerous types, to all of whichhe attached distinctive generic and specific titles in conformity with Linnaeus'then newly-introduced binomial system of nomenclature each of these;compilations, however, possess but minor value compared with the workfirst quoted. To this latter, one is justified, indeed, in conceding as importanta status, as compared with all preceding literature upon the subject, as is subsequentlycommanded by C. G. Ehrenberg's classic volume, 'Die Infusionsthierchen,'published a little over half a century later. As might be anticipated,O. F. Muller embraces in his 'Animalcula Infusoria' numerous minuteorganisms that find no place in the infusorial group as at present constituted,although in this respect he trespasses but slightly from the path subsequentlypursued by Ehrenberg. In all, Muller institutes seventeen genericdenominations, the whole of which are still in use, and only one, his genusCercaria, being founded upon forms not admitted into Ehrenberg's systemof classification, while another, his genus Vibrio, embraces in addition tomany common forms of Bacteria, Vibrio, and Spirillum, as now recognized,various examples of the microscopic hair-worms or Anguillulce. The severalspecies of Stentor were now recognized as members of the same infusorialseries, and transferred to his somewhat comprehensive genus, Vorticella. Asa necessary consequence of the very imperfect instruments available forinvestigation at this early date, little more than a rough general outline ofthe species examined, and no details of their internal organization, areusually recorded, while in many of the types figured the cilia are but representedin part, or even altogether omitted. A reproduction of O. F. Muller'sgeneric subdivisions and earliest proposed scheme of classification of theInfusoria will be found in the chapter hereafter devoted to this specialsubject.In the long interval intervening between the 'publication of Muller's AnimalculaInfusoria 'and the appearance of Ehrenberg's world-famed treatise,a considerable number of investigators occupied themselves in the study ofthese minute organisms, but without achieving any very notable results.