212 Prof. H. James-Clark on the Spongiae ciliatse 



by ciu'ving over the introcepted particles as they pass into the 

 body. The mouth is highly distensible, at times allowing 

 particles as wide as two-thirds the greater diameter of the body 

 to pass in without any apparent extra effort (fig. 51, m). It 

 seems undeniable that it possesses discriminative powers in 

 regard to the quality of its food. This one may readily judge 

 of for himself by seeing the unerring precision with which the 

 particles of floating matter are thrown, by the spasmodic in- 

 curvatm-e of the larger flagelkim, against the mouth, where, if 

 they are not swallowed, they are detained but for an instant 

 by the smaller cilium, quickly adjudged to be worthless, and 

 then thrown off with a twirl of the organ which held them in 

 temporary abeyance. If, however, the captured morsel proves 

 to be agreeable, the larger cilium (fig. 47,/) assists the opera- 

 tions of the smaller one (/*) and the lip, by abruptly bending 

 itself at its point of attachment and laying its basal part across 

 the food, pressing it into the mouth, while the terminal portion 

 is kept in a constant wavy vibration, and cmwed towards the 

 posterior end of the body. This is usually done in three or 

 fom- seconds ; and then the cilia retm-n to their usual positions, 

 while the introcepted edible passes towards the centre of the 

 body, and is there immediately enclosed in a digestive vacuole 

 (fig. 51, d). For a while the food dances about in this vacuole 

 with a very lively motion, but finally it subsides into quietude. 



" The contractile vesicle {cv). — There is a twofold difficulty 

 in discovering the presence of this organ. In the first place, it 

 is comparatively quite small ; and, secondly, it pulsates so 

 slowly that it is very rarely possible to see it contract twice in 

 succession between any two of the abrupt lateral deviations of 

 the body which the spasmodic twitchings of the arcuate fla- 

 gelkim produce. On this account it has not been possible to 

 determine the precise rate of its systole and diastole. It seems 

 to contract from three to four times a minute. It lies near the 

 •surface, about halfway between the two ends of the body, and 

 nearly midway between the two extremes of its greater dia- 

 meter. At the completion of its diastole it has a circular out- 

 line, and appears like a clear colourless vesicle in the midst of 

 the yellowish tissue of the body. Upon contraction it disap- 

 pears, and leaves no trace of its presence. The systole pro- 

 gresses slowly, as in Aiiisonema {A. stdcatum,!)}!^.?, and^.nov. 

 sp. [A. co7icavu7n, §13]), Cyclidium [C. nov. sp.), and Phacus 

 pleuronectes, Duj., and in this respect contrasts strongly with 

 the same process in Heteromita fusiformis, Jas.-Clk., Astasia 

 t ricojyhor a, C\si]). (§12), and Cryptomonas (O. nov. sp.), in 

 which the last half of the systole is very abrupt and marked. 



" The stem. — In addition to what has already been said of 



