212 Prof. H. James-Clark on the Spongie ciliate. 
by curving 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 bod 
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- 
curvature of the larger flagellum, 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 (ff!) 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 curved towards the 
posterior end of the body. ‘This is usually done in three or 
four seconds; and then the cilia return 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 difficul 
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- 
gellum 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 déastole 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 Anisonema (A. sulcatum, Duj.?, and A.nov. 
sp. [A. concavum, §13]), Cyclidium (C. nov. sp.), and Phacus 
pleuronectes, Duj., and in this respect contrasts strongly with 
the same process in Heteromita fusiformis, Jas.-Clk., Astasta 
tricophora, Clap. (§ 12), and Cryptomenas (C. nov. sp.), im 
which the last half of the systole is very abrupt and marked. 
‘¢ The stem.—In addition to what has already been said of 
