36 



ZOOLOGY FOR MEDICAL STUDENTS 



CHAP. 



rounded in form and having its chromatin concentrated in a large 

 central mass. 



In ordinary movement the flagellum acts like that of Euglena — as 

 a tractellum by which the animal is towed along. When moving slowly 



the spiral or conical movement may be 

 seen to be confined to a small portion 

 of the flagellum near its tip while 

 in more rapid movement the whole 

 flagellum is thrown into action. 



The Copromonas feeds on bacteria 

 and other small solid particles of food- 

 material which pass down the oeso- 

 phagus and are ingested by the soft 

 exposed cytoplasm at its inner end. 

 The ingested food-particles soon become 

 surrounded by fluid secreted by the 

 protoplasm and in the food-vacuoles so 

 formed, which usually remain in the 

 neighbourhood of the broad end, the 

 food-material gradually undergoes the 

 process of digestion. 



When a Copromonas is kept under 

 favourable conditions it feeds actively 

 and grows and when the limit of size has 

 been reached it proceeds to reproduce, 

 resolving itself into two individuals by 

 a process of longitudinal fission (Fig. 

 1 6). The flagellum is drawn in ; the 

 nucleus becomes transversely elongated ; 

 the basal granule divides into two — a 

 new flagellum sprouting out from each. 

 A constriction now cuts into the creature 

 from the flagellar end (Fig. i6, 3) ; the 

 reservoir and the nucleus divide into 

 two and as the constriction deepens the 



Copromonas becomes completely divided into two new individuals 



which presently separate and swim away, the whole process taking 



about twenty minutes. 



This reproduction by fission does not go on indefinitely : at a 



variable period (two to six days) it is interrupted by the converse process 



— that of syngamy. 



c.v. 



Fig. 13. 



Copromonas (after Dobell, from Lec- 

 tures on Sex and Heredity, by Bower, 

 Graham Kerr and Agar), c.v, Contractile 

 vacuole ; /, flagellum ; f.v, food-vacuole ; 

 N, nucleus : r, reservoir. 



