STRUCTURE AND LIFE-HISTORY OF COPROMONAS SUBTILIS. 89 
the flagellum is directed backwards along the body, and by 
forcible movement of the anterior end the body is tugged 
round. The only other movements which occur are rolling, 
to a limited extent, caused apparently by a screw-like move- 
ment of the flagellum, and a curious lurching movement 
which .is every now and then observable. It usually occurs 
when the animal is about to turn, but it is difficult to see how 
it is brought about. After progressing steadily and grace- 
fully forward for some distance in a straight line, the monad 
suddenly gives a clumsy lurch sideways ; then, appearing to 
regain its equilibrium, it continues its course, usually in a 
different direction. 
Intrinsic movements do not take place. Owing to the 
rigidity of the surrounding pellicle no “ euglenoid”’ move- 
ments are possible. The pellicle is not contractile, so that the 
contours of the body remain constant. In contrast with 
many other flagellates there is never any tendency to become 
amoeboid. Irregularity of shape is only seen in monads 
undergoing degenerative changes (see infra “ Degenera- 
tion,” p. 102). 
NUTRITION. 
The method of nutrition is holozoic. There can be no 
doubt that the depression at the anterior end of this organism 
—the cytostome—is a true cell mouth. Into this structure 
food particles are being constantly introduced by the forward 
movement of the monad.  Bacilli, micrococci, and minute 
organic particles of all sorts, which are very plentiful in the 
medium in which the monad lives, enter and pass along the 
cytopharynx, and are taken up by the protoplasm at the 
posterior end. Many of the larger bacilli, etc., which enter 
the mouth, and even pass along the pharynx, are not ingested 
but return to the exterior again. If a monad be carefully 
watched for any length of time it will be seen that most of the 
larger particles behave in this way, only the smaller being 
actually ingested. Occasionally an unusually large bacterium 
