434 ORDER FLAGELLATA-EUSTOMATA. 



Its habits are mostly sedentary, the animalcules remaining attached or anchored 

 in social clusters by the temporary adhesion of their gubernacula, and briskly 

 springing to and fro to the full length of their "tether" in various directions. By 

 Ehrenberg this species was first described under the title of Bodo saltans, the 

 same name accompanying the illustrations which alone are given in Stein's recently 

 issued work. 



GENUS III. ANISONEMA, Dujardin. 



Animalcules ovate, free-swimming or temporarily attached, persistent 

 in form, having a more or less indurated cuticular investment ; oral aper- 

 ture distinct, usually followed by a well-defined pharyngeal tract ; anal 

 aperture postero-terminal ; flagellate appendages two in number, of diverse 

 function, originating close to one another on the ventral surface, the ante- 

 rior filament, or tractellum, extended in advance, vibratile, subserving 

 the purposes of locomotion and the capture of food, the posterior flagel- 

 lum, or gubernaculum, trailing in the rear, distally adherent, non-vibratile, 

 utilized during natation as a rudder and also for temporarily attaching the 

 animalcule, cable-wise, to foreign objects ; contractile vesicles and endo- 

 plast conspicuously developed; multiplying by longitudinal fission, and 

 by the production of internal germ-masses. Inhabiting fresh and salt 

 water, and infusions. 



By many recent writers it has been proposed to merge both Heteromita and 

 Heteronema in the present genus, upon the supposition that the softer consistence of 

 the external envelope and contained body-substance in these types represents merely 

 a slightly more marked difference of degree, insufficient for the purposes of generic 

 diagnosis. As demonstrated, however, on a previous page, Heteromita is a perfectly 

 distinct, though isomorphic form, of much lower organization, having no distinct oral 

 aperture, and belonging necessarily to the same Pantostomatous primary group as 

 Monas, Spumella, and Anthophysa. Heteronema, on the other hand, manifests its dis- 

 tinctness from the present genus by the extreme plasticity of its cuticular invest- 

 ment and extraordinary metabolic properties. Evidence supporting the opinion 

 that the members of the genus Anisonema possessed a distinct oral aperture was 

 first adduced by Professor H. James-Clark * who, while unable to demonstrate the 

 exact position of this aperture in A. grande, distinctly saw food -particles pass 

 in at the anterior extremity. This authority likewise suspected the existence of an 

 anal aperture at the posterior end of the body, such anticipation being entirely 

 confirmed by the investigations of the present author, which are again further 

 corroborated by Stein. The determination of the precise position and structure 

 of the oral aperture, with its accompanying well-defined pharyngeal tract, has been 

 recently accomplished by both Stein and O. Butschli. 



Anisonema grande, Ehr. sp. PL. XXIV. FIGS. 26-30. 



Body ovate or oblong, depressed, the dorsal surface slightly convex, the 

 ventral one flat, or more or less concave, rounded posteriorly, narrower and 

 pointed anteriorly, about twice as long as broad ; cuticular investment 

 smooth and indurated ; flagella originating at a little distance from one 

 another close to the anterior extremity, the anterior vibratile flagellum, or 

 tractellum, slender, scarcely equalling the body in length, the trailing 

 flagellum, or gubernaculum, three or four times the length of the other, 

 * 'Memoirs Boston Soc. Nat. Hist.,' 1868. 



