CLASS FLAG ELLA TA. 2 I 7 



more extensive range of structural variation than is met with among the hitherto 

 more familiar Ciliate section of the Infusorial series. 



The foremost place amongst those who by their original investigations have con- 

 tributed most substantially towards our more correct knowledge of this previously 

 comparatively neglected group, must undoubtedly be awarded to Professor Stein in 

 connection with the recently published third volume, Part I., of his magnificent folio 

 series devoted to the description and illustration of infusorial organization. As he 

 himself justly remarks, this volume represents the most important of the three now 

 issued, it dealing exclusively and on the most liberal and comprehensive scale with 

 the class now under consideration. So far, however, Stein's volume is complete 

 with reference only to the illustrations contained in the twenty-four magnificently 

 executed plates, the one hundred and fifty-four pages of text that precede them 

 being devoted chiefly to an exhaustive review of the work achieved by earlier 

 investigators, with relation to both flagellate animal and vegetable organisms, and to 

 a discussion of the claims of the innumerable forms he figures for comprehension 

 among the animal series. A full description of the types there illustrated is reserved for 

 a much looked forward to, but as yet unpublished, second part.* All the species 

 delineated by Stein in the treatise quoted are represented as seen under the high 

 magnification of from 600 to 1200 diameters and upwards, and which is indeed 

 absolutely requisite for gaining a correct estimate of the often highly complex 

 organization of these exceptionally minute beings. As now shown by Stein, numbers 

 of these Flagellata possess not only a well-developed oral aperture, but frequently in 

 addition an extensive pharyngeal dilatation, and in some cases even a buccal or 

 pharyngeal armature comparable to that found in various higher Ciliata. Among 

 the more important features of Stein's work may be also mentioned his comprehen- 

 sion of numerous types belonging to the collared series, first discovered by Professor 

 H. James-Clark here included in the order Choano-Flagellata, and his acquiescence, 

 through such discovery, with the views maintained by Professor Clark, and supported 

 by 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 this 

 class relates merely to the presence of a nucleus and contractile vesicle, without any 

 reference to food-ingesting properties, the result of such lax definition being the 

 admission of such types as Volvox, Gonium, Protococcus (Chlamydococcus), and 

 numerous other forms of whose essential vegetable affinities there is scarcely room 

 for doubt. It is indeed contested by the author (see page 47) whether the types 

 just enumerated possess contractile vesicles ; the inability to detect such structures 

 in numberless examples investigated with the greatest care, being accepted as a 

 conclusive proof of their vegetable nature. 



A conspicuous feature of the reproductive phenomena of the Flagellata 

 is manifested by the tendency of almost all the forms to multiply, in addition 

 to the ordinary process of binary fission, by encystment and the subsequent 

 breaking up of their entire body-mass into sporular elements, such mode of repro- 

 duction being precisely parallel with what obtains among the unicellular plants or 

 Protophytes. Sometimes the spores so produced are few in number and of 

 conspicuous 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 to 

 defy individual definition, even with the assistance of the highest magnifying powers 

 of the compound microscope ; the sporular bodies under such conditions being 

 appropriately designated " microspores." It is further worthy of notice that the 

 production of microspores is more usually preceded by the genetic union or 

 coalescence of two, or it may be many, independent zooids, while that of macro- 



* As a consequence of the present unfinished condition of Stein's monograph, the diagnoses 

 of the innumerable new generic and specific types it embodies, given in this manual, have been 

 framed by the author on the broad characters only indicated in Stein's drawings. The many 

 deficiencies in these diagnoses which must necessarily exist can be supplied only at the hands of the 

 original discoverer of the forms figured. 



