H. JAMES-CLARK ON THE AFFINITIES OF SPONGES. 309 



nence, which constitutes the lip (Ip). The posterior end is either broadly rounded or very 

 bluntly pointed where the pedicel (pd) is attached. The color is either grayish or there 

 is none at all. 



The JlageUum (fl) has more of a sigmoid flexure than that of Monas termo (figs. 1-4), and 

 about as much as that of Anthophi/sa Mullen, Bory (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, Ip), when taking food, 

 and for a propelling apparatus (fig. 5 h ,fl) as the body whirls along after it during natation. 



The mouth (fig. 6, m) lies in the same relative position as that of Monas termo, and receives 

 its food in precisely the same manner, and, by the assistance of the lip (Ip), 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 flagellmn (fl) 

 as that of Monas termo, and at about the same distance from the front, but in an opposite re- 

 gion, and directly in the anteroposterior line with the lip. It is also a more vigorous and 

 larger organ than that of the other Monas, and, bulging out (fig. 5 a , cv) the body even more 

 strongly during expansion, its systole takes place at double the rate, that is, twelve times a 

 minute, 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, pd). Its apex 

 (fig. 5*, pd 1 ) is attached to the posterior end of the body at a point which is coincident with 

 the longitudinal axis. 



§ 3. Bicosceca, nov. gen. 1 (B. gracilipes, nov. sp.) 

 (Plate IX., figs. 34, 35.) 



This genus might be compared to a 3fonas seated in a calyx, and upon a highly muscular, 

 contractile stem. 



Bicosceca gracilipes is a marine form, and has thus far been found, although in considerable 

 numbers, only upon Scriularia cupressina Linn. It is an excessively minute creature ; as 

 may be readily judged by the reader upon referring to the magnifying powers which are 

 laid down in the description of the figures. When first met with it appeared, upon a casual 

 observation, and under a magnifying power of only five hundred diameters, to be an elongate, 

 naked Monas, which was kept in a firm position by some invisible power. It soon, however, 

 attracted particular attention to itself by its peculiar, spasmodic, and often repeated retro 

 cession. Upon putting on a power of eight hundred diameters the whole organization was 

 brought out with sufficient clearness to satisfy one upon every point. For the purposes of 

 illustration, however, it was thought best to increase the magnifying power to a still greater 

 extent, and we have, therefore, drawn one figure (fig. 34) to represent this infusorian as it 

 appears when seen under an amplification of about fifteen hundred diameters. 



This animal has never been found in a free state, nor in any other than that which is 

 represented in these two figures, (figs. 34, 35). It has an elongate oval body which is 

 enclosed in a deep, vasiform, pedicellated calyx (c), to whose bottom it is attached by a slen 



i Siaoc, a vase ; oin£u, to inhabit. 



MEMOIRS HOST. SOC. NAT. HIST. Vol. I. Pt. 3. 2 



