300 ORDER FLAGELLATA-PANTOSTOMATA. 



situated; contractile vesicle not clearly indicated. Length 1-1200" to 

 1-914". HAB. Fresh water. 



The form of the body in this species accords closely with that of the Tetramitus 

 desdssus of Perty, it exhibiting a similar indifferently rounded or sharply pointed 

 posterior conformation, and a corresponding excavation beneath the insertion of 

 the flagella ; the peculiar character of these last-named organs distinguishes it 

 conspicuously from any representative of the Flagellata hitherto described. Although 

 not indicating the existence of a well-defined contractile vesicle, Stein delineates in 

 his several figures of this animalcule a vesicular-like structure near the posterior 

 extremity, upon which, in the accompanying index, the title of an anal aperture is 

 conferred. 



Fam. X. TREPOMONADID-ffi, S. K. 



Animalcules naked, free-swimming, entirely asymmetrical ; flagella two 

 in number, separately inserted ; no distinct oral aperture. 



GENUS I. TREPOMONAS, Dujardin. 



Animalcules free-swimming, exceedingly unsymmetrical in shape, plastic 

 and highly flexible ; irregularly oval, from a dorsal aspect ; thickened poste- 

 riorly, with two anterior, slender, recurved, wing-like lobes as seen in lateral 

 view ; sigmoidal with reversed and pointed extremities viewed apically ; 

 flagella two in number, alike in form and character, produced from the 

 extremity of each of the lateral lobate processes ; contractile vesicle and 

 endoplast conspicuous ; no distinct oral aperture ; movements very rapid, 

 gyratory. Inhabiting stagnant water with decomposing organic matter. 



Trepomonas agilis, Duj. PL. XIX. FIGS. 1-14. 



Body, from a dorsal view (Fig. 12), irregularly oval, broadish anteriorly, 

 more slender and slightly curved posteriorly, with a longitudinal fold 

 towards the left side; in lateral view (Fig. 10), somewhat tongue-shaped, 

 thickest and rounded posteriorly, expanding anteriorly into two symme- 

 trical, laminate, wing-like lobes, which are reflexed backwards to about the 

 centre of the body and terminate each in a single long vibratile flagellum. 

 Apical aspect (Fig. li) broadly sigmoidal, with a thin hyaline border con- 

 necting the recurved points with the thicker body portion ; the flagella 

 continuous from the recurved points; endoplasm transparent, enclosing 

 foreign granules ; contractile vesicle postero-terminal ; endoplast anteriorly 

 situated. Length of body 1-1125". 



HAB. Marsh water with decaying vegetable substances. 



The extraordinarily diverse aspects presented by this animalcule as seen from 

 various points of view, taken together with its minute size and exceedingly active 

 movements in the water, has hitherto presented % an almost insurmountable obstacle 

 to its accurate description and delineation. O. Biitschli,* making a careful investi- 

 gation of this interesting type with the highest available magnifying power and the 

 use of reagents has, however, clearly demonstrated its correct structure and contour, 

 the foregoing diagnosis being framed from his excellent figures and description. The 



* " Beitrage zur Kenntniss der Flagellaten," 'Zeit. Wiss. Zool.,' Band xxx. Heft 2, Jan. 1878. 



