PROTOZOA 



179 



edge of the cover glass and thus makes an air-tight 

 aquarium. I have kept amoeba and some of the smaller 

 infusoria alive in this way over two months. The Para- 

 mcecia usually live only a few days. The preparation must 

 be kept in the light, not sun, so that the plants will give 

 off the oxygen ne- 

 cessary to the life 

 of the animals and 

 also consume their 

 excreted carbon 

 dioxide. 



The movement 

 of the animal is 

 effected by short, 

 hairlike processes 

 (cilia) covering 

 the entire surface. 

 The buccal groove 

 beginning on one 

 side opens into a 

 mouth permitting 

 the food to pass through a short gullet into the soft in- 

 ternal protoplasm (cell contents). They feed largely 

 on bacteria. Near either end of the body may be seen a 

 clear round spot, the contractile vacuole, which is an exit 

 for the surplus water. 



Paramoecium, like all other infusorians, reproduces by 

 binary fission, i.e., divides its body into two equal parts, 

 each of which in a day or two grows to the normal size. 

 This process of division is easily seen, as about a half hour 

 is required for its completion. Each of the new genera- 



FlG. 209. Living Paramcecia photographed through 

 the microscope magnifying eighty diameters. 



