as Infusoria flac-ellata. 189 



mentioned. The Itj) is nearly twice as long in proportion to 

 the breadth of the front as that of B. gracilijjes^ and has an 

 incurved digitate form (figs. 33, 33^, Ijj). 



The. flageUum {fi) 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 bodj ; 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^,/) 

 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, accomjDanied frequently by 

 spasmodic incurvatures, when floating particles are thrown by 

 it towards the mouth {vi). 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,?7^) 

 of food, Avith the aid of the incurvating lip (Ip) and the flagel- 

 lum {f), 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. 33, a) lies in the same hollow as the mouth, but further 

 up on 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 hvo 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. d-. Mag. N. Hist. Ser. 4, Vol.'i. 14 



