af! Infusoria tlagellata. 141 



itself. Within this broad space the simple mouth (m) is 

 situated. 



The Jlagellum [fl) is the most active of the prehensile organs, 

 and the only vibratory filamentous body which this animalcule 

 possesses. In length it is about three times that of the body, 

 or a little more, and projects far beyond the rim of the vase (c). 

 It is a curious fact that while in Monas and Antliophysa the 

 lip and flagellum lie closely together, they stand far apart in 

 Bicosceca. The flagellum is not an undulatory, vibrating 

 organ, in the common sense of the term, but usually supports 

 itself in a rigid condition, except at the tip, which is kept in 

 nearly constant motion, incurvating with frequent jerks, and 

 tossing floating particles toward the mouth. Its distal two- 

 thirds is quite strongly curved, but not so much as to be abso- 

 lutely falcate ; and at its basal third it is moderately arcuated 

 in the opposite direction, so that the whole flagellum has a 

 slightly sigmoid flexure. The plane of this curve is such as 

 to strike the mouth and lip when carried out in that direction. 

 The diameter of this organ is about equal from tip to base, 

 excepting a slight thickening at the latter point. The only 

 times that the flagellum abandons its rigid deportment are either 

 when it is assisting the lip to seize the food, or during the 

 spasmodic retrocession of the body. In the latter case it is 

 abruptly retracted and coiled (fig. S5,^ff) transversely within 

 the calyx (e) close down to the trmicate front of the body. 

 When the latter slowly pushes forward from the bottom of its 

 dormitory, the flagellum as deliberately uncoils, and at first 

 vibrates with a rapid wriggle, but finally assumes its former 

 sigmoid curve and rigid deportment. 



The mouth (m), as has already been mentioned incidentally, 

 lies in the middle of the truncate front, and consequently faces 

 toward the aperture of the calyx (c). Food is brought to it by 

 means of the flagellum (/) ; and the latter and the lip (?^j) 

 force it into the oral aperture exactly in the same way as has 

 been described in regard to Monas. 



The contractile vesicle {cv) is a single globular organ, which 

 lies on the corresponding side of the body with that of Afonas, 

 and just in front of the middle. In full diastole its diameter 

 equals one-third of that of the body. Both the systole and 

 diastole are very slow. 



The calyx (c) is about twice as long as the body which it 

 encloses, and between four and five times its own average 

 diameter. It has the form of a very deep slender m-n, with a 

 rounded bottom, slightly contracted waist, and a very delicate, 

 scarcely reverted, truncate rim. It is so hyaline and faint that 

 it almost defies any magnifying-power below that of eight 

 Ann. & Mag. N. Hist. Ser. 4. Vol.'i. 11 



