232 ORDER FLAGELLATA-PANTOSTOMATA. 



oral aperture has been detected, e. g. Hcrpetomonas, Polytoma, Hexamita, and Tricho- 

 monas. that the animalcules derive their nutriment, as in the case of the Opalinidae, 

 by the direct absorption, at all points, of the proteaceous material held in solution in 

 the fluid media they inhabit. Whether this latter be the haemal or perivisceral fluid 

 of a higher animal, an animal maceration, or a vegetable infusion, protein in its con- 

 centrated and more or less diffused condition is invariably present, and its direct 

 absorption under such circumstances by the contained unicellular animalcules would 

 be strictly analogous to the alimentary process as performed by the individual cell- 

 units of the intestinal tract of all the more highly organized Metazoa. These 

 being>, in fact, live continually immersed within a, so to say, ready prepared bath of 

 nutritive broth, and require no display of energy beyond the passive one of assimila- 

 tion or endosmosis for the satisfying of their creature wants. So far, a group of 

 Flagellata presenting the physiological characteristics here submitted, has been 

 entirely overlooked, its representatives being simply collated with the ordinary 

 mouthed or mouthless species. Even Stein, in his recently published monograph,* 

 erroneously represents such unmistakable Pantostomatous forms as Oikomonas, 

 Spumc//a, and Anthophysa as possessing a well-defined oral aperture. 



'1 he Flagdlata-Piintostomata, in common with the order of the Eustomata, maybe 

 conveniently divided into three minor sections or sub-orders, with reference to the 

 number of flagellate appendages, as indicated in the foregoing schedule. 



A. PANTOSTOMATA-MONOMASTIGA 

 (one flagellum only). 



Fam. I. MONADIDJE, Ehrenberg. 



Animalcules naked or illoricate, entirely free-swimming ; flagellum 

 single, terminal ; no distinct oral aperture ; an endoplast or nucleus and 

 one or more contractile vesicles usually present. 



GENUS I. MONAS, Muller. 



Animalcules free-swimming, exceedingly minute, globose, ovate, or 

 elongate, plastic and unstable in form, possessing no distinct cuticular 

 investment ; flagellum single, terminal ; food-substances incepted at all 

 parts of the periphery, not provided with a distinct mouth ; a nucleus or 

 endoplast and one or more contractile vesicles mostly conspicuous ; multi- 

 plying by longitudinal or transverse fission, or by encystment and the sub- 

 division of the entire substance of the body into a less or greater number 

 of sporular elements. 



Inhabiting salt and fresh water, especially abundant in infusions. 



In the genus Monas, as here delimited, are included the simplest known forms 

 of the typical Infusoria-Flagellata. Its specific representatives exhibit, so far as at 

 present discernible, no higher degree of organization than that of mere specks of 

 more or less granulate and vacuolar nucleated protoplasm, and possess as a locomotive 

 appendage a single thread-like vibratile flagellum. 1 heir extreme simplicity of contour, 

 combined with their very minute size and apparent absence of all readily appre- 

 ciable differential characteristics, necessarily renders it an exceedingly difficult task to 

 discriminate between the innumerable so-called species that have from time to time 

 been referred to this genus. A large proportion of these latter are without doubt 



1 Infusionsthiere, ' Abth. Hi., 1878: Der Flagellaten. 



