REPRODUCTION 



149 



place by wind, attached to soil particles, debris, etc., by the flowing 

 water of rivers or the current in oceans or by insects, birds, other 

 animals to which they become readily attached. When a cyst en- 

 counters a proper environment, a redifferentiation process takes 

 place within the cyst. Various organellae which characterize the 

 organism, are regenerated and reformed, and the trophozoite excysts. 

 The emerged organism once more returns to its trophic phase of 



cm ® ® ® 



Fig. 71. Diagram illustrating the life-cycle of Thelohania legeri (Kudo). 

 a, extrusion of the polar filament in gut of anopheline larva; b, emerged 

 amoebula; c-f, schizogony in fat body; g-m, sporont-formation; m-x, 

 stages in spore-formation. 



existence. Although encystment is a general occurrence among 

 Protozoa, there are some species in which this phenomeonon has 

 never been observed. Paramecium belongs to this group (p. 600). 

 In Sporozoa, no encystment occurs. Here at the end of active 

 schizogony, sexual reproduction usually initiates the production of 

 large numbers of the spores (Fig. 71). 



Sexual reproduction and life-cycles 



Besides reproducing bj' the asexual method, numerous Protozoa 

 reproduce themselves in a manner comparable with the sexual re- 



