REPRODUCTIVE PROCESS IN ANIMALS 55 



(Fig. 32, /) the end of which can be twirled round 

 in such a manner as to draw the creature forwards 

 through the water. The flagellum emerges from the 

 mouth of a slender slightly curved tubular ingrowth 

 of the pellicle, which serves as a gullet down which 

 tiny food-particles are swept by the current sent back 

 by the flagellum. Every now and then a droplet of 

 water laden with such food-particles may be seen to 

 detach itself from the inner end of the gullet, and travel 

 away through the protoplasm, forming a little temporary 

 stomach (Fig. 32, f.v), in which the process of digestion 

 takes place. The water which is taken into the body 

 in this process is eventually drawn out of the protoplasm 

 and ejected into a pocket-like reservoir (Fig. 32, r) 

 connected with the gullet, by a little pump known as the 

 contractile vacuole (Fig. 32, c.v), a bulb of protoplasm 

 which expands and contracts rhythmically. 



The Copromonas under favourable conditions goes on 

 living, feeding and growing. Like other animals it does 

 not increase in size indefinitely, but after a time reaches 

 a rough limit of normal, as we might say, adult size. 

 Its increase beyond this is counteracted by what we 

 recognize as the simplest type of reproductive process- 

 the process known technically as Fission in which the 

 individual simply divides itself into two new individuals, 

 each of half its size. The process is illustrated by the 

 upper portion of Fig. 33. The ordinary adult individual 

 (i) draws in its flagellum (2), and then begins to split 

 longitudinally, the process commencing at the front end 

 (3) and gradually extending until the individual is com- 

 pletely split into two new individuals exactly like itself, 

 except that they are of half its size. It will be noticed 

 that each of the young individuals has grown a new 



