I PHYLUM PROTOZOA 55 



forms the conjugating individuals become completely 

 fused. The effect of the process of conjugation seems to 

 be increased activity in multiplication by fission. 



In mode of life the Infusoria are as varied as the Mastigo- 

 phora. Some are holozoic, some saprophytic, some parasitic. 

 Of the parasitic forms some give rise to definite diseases 

 in the bodies of their hosts. The skin-affection known as 

 eczema, for example, seems to be caused by the presence of 

 parasitic Vorticellae. 



4. THE SPOROZOA. 



In the interior of certain organs termed the seminal 

 vesicles of the Earthworm will often be found a parasitic 

 Protozoan Monocystis agilis (Fig. 23) which exemplifies 

 another of the classes of the phylum, the class Sporozoa. 

 It is flattened, elongated, pointed at both ends, and performs 

 slow movements of expansion and contraction (A, B\ 

 reminding us of those of Euglena. There are neither 

 pseudopodia, nor flagella, nor cilia. There is a firm 

 cuticle, and the protoplasm is divided into a denser 

 superficial portion, the cortex, and a central semi-fluid mass, 

 the medulla. There is a large clear nucleus, but no trace of 

 contractile vacuole, or of mouth or gullet. Reproduction 

 takes place by a peculiar and characteristic process of spore- 

 formation. Either a single individual, or two individuals 

 closely applied together but not actually fused, become 

 encysted. Multiple fission then takes place, the proto- 

 plasm becoming divided (C) into an immense number of 

 spindle-shaped spores, each surrounded by a strong 

 chitinoid coat, and thus differing markedly from the naked 

 spores of Rhizopoda and Mastigophora. The protoplasm 

 of each spore then undergoes fission, becoming divided 



