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( 49 )CHAPTER III.NATURE AND ORGANIZATION OF THE INFUSORIA.PROCEEDING to the more immediate consideration of the special group orgroups of organisms that form the subject-matter of this volume, it is in thefirst place scarcely requisite to observe that the title of the Infusoria asemployed from the date of its earliest introduction up to the present timehas carried with it a most wide and indeterminate meaning. Formerlyutilized for the distinction of almost every microscopically minute aquaticorganism, whether belonging to the animal or vegetable series, it is foundto embrace for the most part in its more modern application several highlydifferentiated classes or sections of the sub-kingdom Protozoa, and in somecases, even yet, organisms whose true position should undoubtedly be amongthe representatives of the vegetable world. In accordance with the viewsheld by the present author, the Infusoria as a group, even when restricted toforms exhibiting a decided animal organization only, scarcely possesses anintrinsic or coherent status, embracing as it does, though incompletely,representatives of all four of the primary natural sections of the Protozoathat have been previously enumerated. Adapted, however, as closely aspossible to meet existing exigency, this same group or legion, as it maybe conveniently denominated, corresponds as here embodied most closelywith those three classes of the Protozoa included in the preceding tabularview of this sub-kingdom under the titles of the Flagellata, Ciliata, andTentaculifera. In other words, it comprehends, with the exception ofthe typical Rhizopoda and two subordinate Flagellate orders of theSpongida and Mycetozoa, the whole of the representatives of the Protozoa.if not the second, of theseBut for the limits of space at command, the first,have been admitted and describedtwo last-named orders would likewisein extenso on equal terms with their associated groups ;its individual representatives,as explained at length in Chapter V., conforming in all essentialstructural and developmental details with those of that special order heredistinguished by the name of the Choano-Flagellata. From the evidencealready submitted, it is clearly apparent that the Infusoria, from whicheverpoint of view selected, can be regarded as irregularly gathered excerptsonly from that primary subdivision of the animal kingdom known as theProtozoa, and that no correct estimate of the affinities nor definition of thecharacters of its multitudinous representatives can be accomplished apartfrom their consideration as constituent integers of this one harmoniousE