GENUS BICOSCECA. 275 



primary origin of tlie contractile pedicle as an altogctlier independent tail-like 

 prolongation of the posterior region is clearly manifested. Stein* substitutes the 

 title of Bikceca for this genus as more etymologically correct. 



Bicosoeca lacustris, J.-Clk, Pl. XVIII. Figs. 13-19. 



Lorica elongate-ovate, widest posteriorly, a little over twice as long as 

 broad, supported on a pedicle which nearly equals it in length ; animalcule 

 when extended projecting beyond the aperture of the lorica, produced 

 anteriorly in the form of a projecting lip-like prominence, attached 

 posteriorly to the bottom of the lorica by an eccentrically developed, 

 thread-like, contractile ligament ; flagella uneven, one long and one short, 

 the longer one when retracted rolled spirally within the cavity of the 

 lorica ; contractile vesicles two or three in number, posteriorly situated ; 

 endoplast spherical, subcentral. Length of lorica 1-2500". 



Hab. — Pond water ; abundant. 



This species represents, undoubtedly, one of the most widely distributed members 

 of the Flagellata, it having been met with by the author in more or less abundance 

 on weeds from almost every sample of pond-water examined. The i)resence of 

 the second and comparatively very short flagellum is difficult to determine without 

 the employment of a high magnifying power of the microscope (800 diameters and 

 upwards) and a careful manipulation of the illuminating agency. In the descriptions 

 illustrative of this type, indeed, as originally given by H. James-Clark, or more 

 subsequently by Stein or Biitschli, a single long flagellum only is reported to exist. 

 The possession of a minute supplementary appendage has, however, been repeatedly 

 corroborated, and more recently with the advantage of verification by an indepen- 

 dent witness. Even where not distinctly visible, its presence is clearly indicated by 

 the tremulous motion of the particles in the vicinity of the much attenuated lip-like 

 prominence, and behind which process of the anterior region this smaller flagellum 

 is frequently more or less completely concealed. The posterior and retractile 

 thread-like ligament securing the animalcule to its lorica in this species is inserted 

 eccentrically, and towards the ventral aspect— a circumstance, however, which is 

 distinctly shown only when a lateral view, as indicated at PI. XVIII. Fig. 19, 

 is presented. On retreating into its lorica, this thread-like ligament or peduncle is 

 folded tightly on itself, while the longer of the two flagella, as shown at Fig. 17, 

 is thrown into an elegant spiral coil, reminding the observer of the spirally retracted 

 proboscis of a butterfly. The ingestion of food-particles has been observed to take 

 place indifferently at all points of the exposed anterior border, against which region 

 they are cast by the vibrating motions of the long flagellum, the shorter appendage 

 apparently assisting in making further secure the food-substances brought within 

 reach by the longer one. 



The most general method of reproduction exhibited by Bicosceca lacustris, in 

 common with the other representatives of the same genus, is that of multiplica- 

 tion by transverse fission. Preceding such duplicative process, the body of the 

 animalcule, growing to nearly twice its normal size, almost completely fills the 

 cavity of the lorica ; a transverse furrow then makes its way across the centre, 

 increasing in depth until the anterior moiety becomes completely separated from 

 the hinder one, and is liberated into the outer water. Within the course of a 

 few minutes, the posterior portion, which is left attached to the contractile pedicle, 

 develops two new flagella, and has assumed a contour in every way identical with 

 that which the animalcule originally possessed. The detached anterior half issuing 

 from the aperture of the lorica, immediately takes upon itself the form and habits 

 of a free-swimming zooid, altogether unlike the parent, and most nearly resembling 



* ' Infusionsthiere,' Abth. iii., 1878. 



T 2 



