310 II. JAMES-CLARK ON THE AFFINITIES OF SPONGES. 



der, colorless, contractile ligament (r). It usually rests about halfway between the top and 

 bottom of the calyx, but is frequently jerked to the bottom (fig. 35) of the vase (c) by means 

 of the ligament just mentioned. The anterior end is truncate, and prolonged into two 

 prehensile organs, one of which is a flageUum (ft and the other a lip (lp) similar in position 

 and function to that of the Monas described in the previous section. The generally prevailing 

 fuscous tint is interrupted by a transparent, colorless streak (r 1 ) which extends from the lat- 

 erally posited base of the flageUum (ft to the posterior end of the body, where it seems to 

 be prolonged into the contractile ligament (r). It is not a band, however, but a sharply 

 defined furrow, of considerable depth. At the anterior end it is sunk so deeply that it 

 borders closely upon the base of the flageUum, and from that point it gradually 'shallows 

 until it nearly disappears at the point of junction of the body with the contractile h>a- 

 ment. ° 



We are thus reminded of those heteronematous flagellMa, like Anisonema (figs. 65-69) 

 whose bodies are so conspicuously sulcated in a longitudinal direction ; and the apparent 

 continuation of the retractor ligament (fig. 34, r) with this furrow (r 1 ) heightens the impres- 

 sion, by its resemblance to the highly muscular, trailing lash (figs. 65-69,/ 2 ) of that genus 

 One could hardly be accused of unduly straining a point in homology if he were to con- 

 sider the furrow (fig. 34, r 1 ) in question as merely a greatly prolonged ostial notch, and the 

 retractor (r) as a trailing lash, which originated at the greatest possible distance from the 

 other, its proboscidal companion (/). 



The lip (lp) is a more prominent organ than that of Monas. It has a conical shape, and is 

 about twice as long as its greatest breadth. It is so hyaline as to readily escape notice 

 until it is fully recognized. It is situated at the edge of the truncate front opposite to that 

 from which the flageUum arises, and therefore leaves a considerable space between the latter 

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



The flageUum (ft) is the most active of the prehensile organs, and the only vibratory, fila- 

 mentous 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 Anihophysa the lip and flageUum lie closely together, they stand 

 far apart in Bicosmca. The flageUum is not an undulatory, vibrating organ, in the com- 

 mon 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 float^ 

 ing particles toward the mouth. Its distal two thirds is quite strongly curved, but not so 

 much as to be absolutely falcate; and at its basal third it is moderately arcuated in the opposite 

 direction, so that the whole flageUum 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 flageUum abandons its rigid deportment is 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. 35, /) transversely within the calyx (c) close 

 down to the truncate front of the body. When the latter slowly pushes forward from the 

 bottom of its dormitory, the flageUum 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 trun- 

 cate front, and consequently faces toward the aperture of the calyx (c). Food is brought 



