68 ORGANIZATION OF THE INFUSORIA. 



The most remarkable type of oral armature possessed by the series of 

 organisms now under consideration is, undoubtedly, met with in the Dystcria 

 arinata of Professor Huxley, in which the simple corneous tube or tubular 

 rod-fascicle of its nearest associates is, as fully recorded in the description 

 given of this specific form, replaced by a series of corneous plates and 

 styles of such diverse and complex character that considerable doubt was 

 entertained at the date of its discovery as to whether the organism might 

 not be more correctly relegated to the section of the Rotifera. Following 

 upon the oral aperture, it not unfrequently happens that a secondary tubular 

 passage, conveniently though incorrectly termed the " pharynx " — it being in 

 no way homologous with that structure as developed in Metazoic organisms 

 — penetrates still deeper into the substance of the central endoplasm, 

 and serves as a channel for the conduct of incepted food-substances to this 

 region. An example of such a prolonged pharyngeal passage, its distal 

 termination at the same time exhibiting a somewhat remarkable hook-like 

 curvature, characterizes Cohn's genus Helicostomiim. In many instances, 

 such as Cliniacostonmni and the type last named, this pharyngeal prolonga- 

 tion is entirely smooth throughout, while in others, such as Nyctotherus and 

 MetopHs, it is more or less distinctly ciliate. The most complex form of 

 oral and pharyngeal organization is, however, met with in certain of the 

 Peritrichous representatives of the Ciliata. Here, as demonstrated by Greeff, 

 more especially in the cases oi Epistylis flavicans diWd plicatilis, the prolonged 

 and thickly ciliated pharynx is followed by an almost equally long but 

 exceedingly slender and non-ciliate tubular canal, or so-called " oesophagus," 

 whose distal termination is suspended freely in the central fluid endo- 

 plasm. At the point of junction of the pharynx with the above narrower 

 canal-like prolongation this latter structure exhibits a peculiar bulb-like 

 dilatation into which the food-particles fall after their passage through 

 the wider superior portion, and are there moulded into the characteristic 

 pellet-like masses which are to be seen regurgitating through the sub- 

 stance of the body. The foregoing type of oral and oesophageal organization 

 has been recently shown by Wrzesniowski to obtain in Ophrydiiim versatile, 

 and is apparently common to all the members of the Vorticellidan family. 

 In the genus Didiniiim, the inner lining of the oral region can be protruded 

 to a considerable distance, after the manner of a proboscis, for the purpose 

 of food-capture ; a like, though somewhat less pronounced, structural 

 modification is met with in Mesodinium. 



A nal Aperture or Cytopyge. 



The results of recent investigation have tended to demonstrate that a 

 distinct anal aperture, or as Haeckel denominates it the "cytopyge," for 

 the discharge of faecal substances, exists in at least all of the Eustomatous 

 section of the Infusoria, while in not a few of the Pantostomata, such a 

 distinct aperture is, although not distinctly developed, most clearly fore- 



