136 Prof. H. James-Clark on the Spongise ciliataj 



fixed state (fig. 3), and tlie other a free and motile stage (figs. 1, 

 2, 4). Dm-ing its sedentary life, it may be found in great 

 abmidance on the old stems of Myriophyllum^ Potamogeton^ 

 Ceratojpliyllum^ and other aquatic phgenogamous plants which 

 inhabit quiet waters, and are more or less thickly covered by a 

 floccose overgrowth of various minute Confervaj, Diatomaceae, 

 &c. In its free state it swims with either a sort of hitching, 

 wriggling motion, or, gliding along smoothly, revolves at an 

 inconstant but never rapid rate upon its longer axis, of which 

 the flagellum (fig. 2/), which always precedes it, maybe said 

 to be a prolongation. This is the condition in which it is 

 most frequently to be fomid after it has been kept a few days 

 in an aquarium. It then gathers in swarms about decomposing 

 matter, and thus affords frequent opportunity of seeing its mode 

 of collecting and swallowing its food. 



The form of the body in a fixed state (fig. 3) may be com- 

 pared to a flattened heart, of which one summit is prolonged 

 into a broad, conical, transparent beak (^:>), and at the opposite 

 end the apex is attached to a slender, flexible pedicel {pd)^ 

 wdiich frequently is equal in length to four or five times the 

 antero-posterior diameter of the body. In a free condition 

 (fig. 2) the posterior end is rounded and about as broad as the 

 front, but still it presents the same lateral flattening as the 

 fixed form. The prevailing colour is a faint olive or yellowish 

 green. 



The flagellum {fl) is the only cilium-like organ which this 

 creature possesses. It is attached to the front, close to the 

 proximal side of the conical beak {Ijy), and consequently lies 

 in the axial line of the body. In a quiet state, which it most 

 frequently assumes during the fixed condition, it appears like 

 an arcuate bristle, and extends from near its base to its apex 

 in one uniform, slightly but distinctly curved line, and termi- 

 nates without any very sensible diminution in thickness. The 

 plane of its curve is in direct extension of the plane of the 

 greater diameter of the body, and at the same time passes 

 through the conical beak. During natation the flagellum 

 takes precedence and vibrates with an undulating Avhirling 

 motion which is most especially observable at its tip, and 

 produces by this mode of propulsion the peculiar rolling of the 

 body which at times lends so much grace to its movements as 

 it glides from place to place. During the fixed state of the 

 body the chief design of the movements of the flagellum is the 

 prehension of food ; and this is accomplished by a peculiar 

 abrupt deflection of the end of this organ towards the front, 

 by means of which particles of various kinds are made to im- 

 pinge upon the region immediately at the proximal side of the 



