492 ORDER HOLOTRICHA. 



taking the form of a simple corneous tube; contractile vesicle mostly single, 

 located close to the anal aperture; cortical layer sometimes enclosing 

 trichocysts. 



The apical position of the oral aperture alone distinguishes the representatives 

 of this genus from those of A^assida. Most of the species frequent pond and 

 stagnant water. Their motion in the water is rapid, and chiefly rotatory on the 

 longitudinal axis. One form only is as yet recorded as having a marine habitat. 



Prorodon niveus, Ehr. Pl. XXVI. Figs. 36 .and 49. 



Body elliptical, compressed, about twice as long as broad, oral aperture 

 terminal ; pharjmgeal armature consisting of a short, compressed fascicle 

 of numerous closely approximated rod-like teeth ; endoplast band-like, 

 curved, often S-shaped ; contractile vesicle single, spherical, postero-terminal ; 

 no trichocysts ; colour white. Length of body 1-72". 



Hab. — Bog water, amongst Confervce. 



The large size of this animalcule, and the high development of the phar)'ngeal 

 armature, readily distinguish it from the other members of the genus. Seventy 

 and eighty-three of the characteristic rod-like teeth are reported by Ehrenberg as 

 being respectively present in the one half only of the rod-fascicles exposed to view in 

 two examples that were made the subject of careful examination. 



Prorodon teres, Ehr. 



Body ovate, cylindrical, twice as long as broad, slightly narrowed 

 anteriorly ; oral aperture exactly terminal ; pharynx enclosing an elongate 

 cylindrical fascicle of rod-like teeth ; endoplast ovate ; contractile vesicle 

 single, postero-terminal ; no trichocysts. Length of body 1-140". 



Hab. — Pond water. 



The cyhndrical fascicle with which the pharyngeal cavity of this species is 

 strengthened has been estimated to contain from twenty to as many as forty-five of 

 the characteristic rod-like teeth. Encystment, accompanied by the partition of 

 the animalcule into two equal halves within its cyst, has been reported by Cohn.* 



Prorodon griseus, C. & L. 



Body ovate, cylindrical, rounded at the two extremities, slightly the 

 widest anteriorly, from two to two and a half times as long as broad ; 

 cuticular surface finely and closely striate longitudinally ; oral aperture 

 subterminal ; pharyngeal rod-fascicle large, cylindrical, slightly curved ; 

 endoplast oval, enclosing a small endoplastule ; contractile vesicle single, 

 postero-terminal, of large size ; colour clear brown when viewed as a 

 transparent object, white by reflected light ; no trichocysts. Length of 

 body 1-250". Hab. — Stagnant water: Berlin (ClaparMe and Lachmann). 



Prorodon armatus, C. & L. 



Body nearly globular, slightly compressed, oral aperture subterminal ; 

 pharyngeal rod-fascicle cylindrical, wide, and comparatively short ; endoplast 



* 'Zeitschrift fiir Wissenschaftliche Zoologie,' Bd. iii., 1S53. 



