GENUS OPISTHODON. 749 



cilia bordering the adoral groove ; marginal setje very short and fine, 

 scarcely equalling the cilia in length ; parenchyma tawny yellow, highly 

 vacuolar ; contractile vesicles numerous, posteriorly situated (?) ; endo- 

 plasts numerous, spherical, usually with laterally attached endoplastules, 

 distributed throughout the length of the parenchyma, and connected with 

 each other by a cord-like filament or funiculus ; a row of spherical refringent 

 corpuscles usually developed in the vicinity of the right-hand margin of 

 the anterior region of the body ; animalcules swimming evenly or rotating 

 on their axis and creeping over foreign substances. Length 1-150' to 1-50". 

 Hab. — Stagnant water. 



The vacuolation of the substance of the parenchyma in this species closely 

 resembles that of Trachelius ovum or Noctiliica, and is sometimes developed to such 

 an extent as to leave beneath the cuticular surface a mere network of protoplasmic 

 trabecute. As a rule, the vacuolation is most conspicuous towards the posterior ex- 

 tremity. The incepted food-particles transported from the oral region pass freely 

 into this protoplasmic network and are retained within its substance, in no case 

 intruding into the intervening vacuolar spaces. Claparfede and Lachmann, in 

 accordance with the more highly organized multicellar structure claimed by them 

 for the Ciliate Infusoria, have conceded to this food-enclosing network the function 

 of a tubular, ramifying, membrane-bounded intestinal tract, allotting at the same time 

 to the intervening lacunae the role of a rudimentary abdominal cavity. The incon- 

 stant character of this vacuolar system, however, it presenting a diverse aspect in 

 different examples, and not being permanent in character in even the same animal- 

 cules, sufficiently demonstrates the untenability of this interpretation. The possession 

 by LoxOiies rostrum of distinct contractile vesicles has not up to the present time been 

 definitely established. Clapar^de and Lachmann are, however, inclined to regard as 

 equivalent to such structures the rounder and more persistent vacuolae developed at 

 the posterior extremity of the body, and record the periodic inflation and contraction 

 of this entire region. As first pointed out by Johannes Miiller, some structures of 

 a peculiar and as yet unexplained nature are found attached to the inner surface of 

 the cortical parenchyma ; these are of spherical shape, clear and transparent, enclose 

 a central nucleolarlike body, and are distributed in an even line adjacent to and 

 parallel with the right marginal border. A possible secretive function has been rele- 

 gated to these bodies by Claparede and Lachmann and other authorities. The 

 racemose development of the numerous spherical endoplasts or nuclei, with their 

 attached endoplastules, is best illustrated, as demonstrated by Wrzesniowski, see 

 PI. L. Fig. 14, through the employment of a one per cent, solution of acetic acid. 

 In many instances, as pointed out by the last-named authority, the endoplastule, 

 instead of being affixed to the endoplast, is found attached separately to the 

 connecting cord or funiculus, while in other cases it may be entirely absent. The 

 specialized corneous armature of the pharynx and adoral groove, interpreted 

 correctly in the first place by Engelmann, was noticed and described by earlier 

 observers as a mere local aggregation of dark -brown pigment-granules. The peculiar 

 hue of this structure, dark chestnut brown in adult examples, and more transparent 

 in younger individuals, is at once suggestive of the similarly coloured corneous loricae 

 of various Vaginicolinse ; the chemical composition of the t\vo is probably identical. 



Genus IV. OPISTHODON, Stein. 



Animalcules free-swimming, ovate or egg-shaped, the dorsal surface 

 more or less convex, the ventral surface plane, entirely ciliate ; oral aperture 

 situated towards the posterior half of the body, supplemented by a cylin- 

 drical pharyngeal rod-fascicle. Inhabiting fresh water. 



