as Infusoria flagellata. 189 
mentioned. The lip is nearly twice as long in proportion to 
the breadth of the front as that of B. gracilipes, and has an 
incurved digitate form (figs. 33, 334, (p). 
The flagellum (fl) is the most remarkable and distinguishing 
feature of this species, when contrasted with B. gracilipes, on 
- account of the wide angle at which it diverges from the longi- 
tudinal axis of the body; for whilst in the latter it deviates 
but little from parallelism with the axial line, in the former it 
arises at an angle of from forty to forty-five degrees (fig.33*, f) 
with the same line. At its base it curves away from the lip, 
but for the remaining four-fifths it bends with a long arch in 
the opposite direction, but not so much as to bring its tip in a 
line with the body. It is therefore altogether eccentric; but 
yet its curve lies in the same plane relatively to the mouth 
and lip as that of its marine congener. Its length is about 
two and a half times that of the body; and it scarcely, 
if at all, tapers from one end to the other. It usually 
is held in a rigid attitude, except at the tip, which is always 
kept in a rapidly gyrating state, accompanied frequently by 
spasmodic incurvatures, when floating particles are thrown by 
it towards the mouth (m). Its flexibility is exhibited during 
the frequent spasmodic retrocessions of the body (fig. 33°), in 
the same way as in the other species; and the like remark | 
applies to its action when assisting the lip to force the food 
into the mouth. 
The mouth (m) opens in a slight hollow which lies between 
the base of the flagellum on one side and the lip on the other, 
and therefore is concentric with the longitudinal axis of the 
body. It very readily takes in quite large particles (fig.33,m) 
of food, with the aid of the incurvating lip (/p) and the flagel- 
lum (#1), and immediately encloses them in a digestive vacuole, 
or, more properly speaking, a hyaline envelope, within which 
they revolve for a while with considerable rapidity. The anus 
(fig. 83, a) lies in the same hollow as the mouth, but further 
___ upon the base of the lip. That it is distinct from the mouth 
was frequently demonstrated by the collection of large globular 
masses In the base of the lip, and sometimes further up, and 
their subsequent exit thereabouts. 
The two contractile vesicles (cv, cv) form another very strong 
mark of distinction, since they are not only double the number 
of that of B. gracilipes, but are also situated at the extreme 
__. posterior end of the body. They are quite conspicuous, and 
appear to lie right and left of the plane which passes through 
the lip, flagellum, and furrow. The systole of each alternates 
with that of the other, and occurs from five to six times in a 
Ann. & Mag. N. Hist. Ser. 4. Vol. i. 14 
