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CLASS FLAGELLA TA. 2 I7more extensive range of structural variation than is met with amongthe hithertomore familiar Ciliate section of the Infusorial series.The foremost place amongst those who by their original investigations have contributedmost substantially towards our more correct knowledge of this previouslycomparatively neglected group, must undoubtedly be awarded to Professor Stein inconnection with the recently published third volume, Part I., of his magnificent folioseries devoted to the description and illustration of infusorial organization. As hehimself justly remarks, this volume represents the most important of the three nowissued, it dealing exclusively and on the most liberal and comprehensive scale withthe class now under consideration. So far, however, Stein's volume is completewith reference only to the illustrations contained in the twenty-four magnificentlyexecuted plates, the one hundred and fifty-four pages of text that precede thembeing devoted chiefly to an exhaustive review of the work achieved by earlierinvestigators, with relation to both flagellate animal and vegetable organisms, and toa discussion of the claims of the innumerable forms he figures for comprehensionamong the animal A series. full description of the types there illustrated is reserved fora much looked forward to, but as yet unpublished, second part.* All the speciesdelineated by Stein in the treatise quoted are represented as seen under the highmagnification of from 600 to 1200 diameters and upwards, and which is indeedabsolutely requisite for gaining a correct estimate of the often highly complexorganization of these exceptionally minute beings. As now shown by Stein, numbersof these Flagellata possess not only a well-developed oral aperture, but frequently inaddition an extensive pharyngeal dilatation, and in some cases even a buccal orpharyngeal armature comparable to that found in various higher Ciliata. Amongthe more important features of Stein's work may be also mentioned his comprehensionof numerous types belonging to the collared series, first discovered by ProfessorH. James-Clark here included in the order Choano-Flagellata, and his acquiescence,through such discovery, with the views maintained by Professor Clark, and supportedby the author, respecting the affinities of the sponges. The limits assigned to the>Flagellata by Professor Stein differ essentially from those recognized in this treatise.As already notified at page 197, the fundamental basis upon which he establishes thisclass relates merely to the presence of a nucleus and contractile vesicle, without anyreference to food-ingesting properties, the result of such lax definition being theadmission of such types as Volvox, Gonium, Protococcus (Chlamydococcus), andnumerous other forms of whose essential vegetable affinities there is scarcely roomfor doubt. It is indeed contested by the author (see page 47) whether the typesjust enumerated possess contractile vesicles the; inability to detect such structuresin numberless examples investigated with the greatest care, being accepted as aconclusive proof of their vegetableA nature.conspicuous feature of the reproductive phenomena of the Flagellatais manifested by the tendency of almost all the forms to multiply, in additionto the ordinary process of binary fission, by encystment and the subsequentbreaking up of their entire body-mass into sporular elements, such mode of reproductionbeing precisely parallel with what obtains among the unicellular plants orProtophytes. Sometimes the spores so produced are few in number and ofconspicuous size, meriting the title, as here applied to them, of " macrospores " while;in other instances they are altogether innumerable, and of such minute calibre as todefy individual definition, even with the assistance of the highest magnifying powersof the compound microscope the; sporular bodies under such conditions beingappropriately designated " microspores." It is further worthy of notice that theproduction of microspores is more usually preceded by the genetic union orcoalescence of two, or itmay be many, independent zooids, while that of macro-* As a consequence of the present unfinished condition of Stein's monograph, the diagnosesof the innumerable new generic and specific types it embodies, given in this manual, have beenframed by the author on the broad characters only indicated in Stein's drawings. The manydeficiencies in these diagnoses which must necessarily exist can be supplied only at the hands of theoriginal discoverer of the forms figured.