H. JAMES-CLARK ON THE AFFINITIES OF SPONGES. 307 



inconstant but never rapid rate upon its longer axis, of which the flagellura (fig. 2,fl), 

 which always precedes it, may be said to be a prolongation. This is the condition in which 

 it is most frequently to be found 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 see- 

 ing its mode of collecting and swallowing; its food. 



The form of the body in a fixed state (fig. 3) may be compared to a flattened heart, of 

 which one summit is prolonged into a broad, conical, transparent beak (/j>), and at the oppo- 

 site end the apex is attached to a slender, flexible pedicel {pd), which 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 color is a faint olive or yellowish 

 green. 



The flagellum (fl) is the only cilium-like organ which this creature possesses. It is at- 

 tached to the front, close to the proximal side of the conical beak (Jp), and consequently 

 lies in the axial line of the body. In a quiet state, which it most frequently assumes dur- 

 ing 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 terminates 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, 

 whirling 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 accom- 

 plished by a peculiar, abrupt deflection of the end of this organ toward the front, by means 

 of which particles of various kinds are made to impinge upon the region immediately at 

 the proximal side of the base of the broad, conical beak; — a point at which, as will be seen 

 presently, the mouth is situated. 



The mouth (figs. 3, 4, m) lies between the base of the flagellum (/) and the beak, or lip 

 (Jp), as I shall hereafter designate it, from its obvious office, presently to be described. A 

 plane, therefore, drawn through the lip and the base of the flagellum, would also strike the 

 mouth, and moreover form a continuation of that of the greater diameter of the body. 

 This aperture is not visible during its closed state, but its presence has been often and un- 

 mistakably determined by seeing the masses of food enter invariably at the point desig- 

 nated above. As already stated, particles are thrown with a sudden jerk, precisely as is done 

 by Antkophysa Mulleri, Bory. (figs. 50, 51), and apparently with great precision, directly 

 against the mouth (fig. 4, m). If acceptable for food, the flagellum presses its base down 

 upon the morsel, and at the same time the lip is thrown back (fig. 4, Ip) so as to disclose the 

 mouth, and then bent over the particle as it sinks into the latter. When the lip has ob- 

 tained a fair hold upon the food, the flagellum withdraws from its incumbent position and 

 returns to its former rigid, watchful condition (fig. 4,fl). The process of deglutition is then 

 carried on by the help of the lip alone, which expands laterally until it completely overlies 

 the particle. All this is done quite rapidly, in a few seconds, and then the food glides 

 quickly into the depths of the body, and is enveloped in a digestive vacuole (d), whilst the 

 lip assumes its usual conical shape and proportions. 



