as Infusoria flagellata. 139 



The JlageUu77i (Jl) has more of a sigmoid flexure than that 

 oi Monas terono (figs. 1-4), and about as much as that oi An- 

 thophysa Millleri^ ^OYj (figs. 47, 48,^^). It arises from the 

 axial point of the front, and extends to about three times the 

 length of the body. The plane of its curve bears the same 

 relation to the mouth and lip as that of Monas termo^ and it is 

 used in the same manner as a prehensile organ to assist the 

 lip (fig. 6, /p) when taking food, and for a propelling-apparatus 

 (fig. S^ifl)i as the body whirls along after it during natation. 



The mouth (fig. 6, m) lies in the same relative position as 

 that of Monas tenno, and receives its food in precisely the same 

 manner, and, by the assistance of the lip (/^), with the same 

 degree of rapidity passes it into the body. 



The contractile vesicle (cv) lies on the same side of the plane 

 of the arcuate flagellum (Jl) as that of lianas termo, and at 

 about the same distance from the front, but in an opposite 

 region, and directly in the antero-posterior line with the lip. 

 It is also a more vigorous and larger organ than that of the 

 other Monas ; and, bulging out (fig. 5^, cv) the body even more 

 strongly during expansion, its systole takes place at double 

 the rate (that is, tivelve times a minute) j and very abruptly. 



The pedicel {pd ) sometimes attains to four or five times the 

 length of the body, but most frequently it is not more than half 

 as long as that. It is thin and delicate, but appears to possess 

 considerable rigidity, either in a fully extended state, or when 

 (as appears to be the case sometimes) it is contracted into more 

 or less abrupt curves (fig. 6,^jrf). Its apex (fig. 5% 7;^^) is 

 attached to the posterior end of the body, at a point which is 

 coincident with the longitudinal axis. 



§ 3. BicoscECA, nov. gen.* 

 Bicososca gracilipes, nov. sp. PI. V. figs. 34, 35. 



This genus might be compared to a Monas seated in a calyx, 

 and upon a highly muscular, contractile stem. 



Bicososca gracilipes is a marine form, and has thus far been 

 found, although in considerable numbers, only upon Sertularia 

 cupressina^ Linn. It is an excessively minute creature, as may 

 be readily judged by the reader upon referring to the magnify- 

 ing powers which are laid down in the description of the 

 figures. When first met with, it appeared, upon a casual ob- 

 servation and under a magnifying-power of only five hundred 

 diameters, to be an elongate, naked 3fonas, which was kept in 

 a firm position by some invisible power. It soon, however, 

 attracted particular attention to itself by its peculiar, spasmodic 



* ^LKos, a vase ; oIk£(o, to inhabit. 



