104 



PROTOZOA. 



of animals ; often, especially when young, within the cells of their host ; 

 deriving their food by absorbing diffusible juices. A single large nucleus ; 

 no contractile vacuole. Reproduction by division in early life, but 

 typically by spore formation. An encysted phase precedes the division 

 into encased spores. The young forms escaping from a spore case may 

 be flagellate or amoeboid ; but, except in a very few cases, passivity pre- 

 vails, and the adults are much restricted in their contractile movements. 

 Conjugation, followed by fusion, often precedes encystation ; and two 

 forms often occur joined together but not fused. 



Examples. Monocystis, in earthworm ; Gregarina^ with a cross par- 

 tition, in food canal of Arthropods ; Eimeria, remaining, except in young 

 stages, within a cell of the host ; Drepanidium, and other forms, in blood 

 corpuscles ; Myxiditun, with amoeboid adult ; Sarcocystis, in muscle 

 fibres of Mammals and some other Vertebrates ; Coccidium ovifonne, a 



FIG. 30. A Colonial Flagellate Infusorian Proterospongia 

 Hseckelii. (After SAVILLE KENT.) 



There are about 40 flagellate individuals. , nucleus ; 6, contractile 

 vacuole ; c, amoeboid unit in gelatinous matrix ; d, division of an 

 amoeboid unit ; , flagellate units with collars contracted ; f, hyaline 

 outer membranes ; g, unit forming spores. 



permanent cell parasite, in many Vertebrates, common in the liver of 

 rabbits, &c. 



jD. Predominantly Active Forms (ciliate and flagellate), 

 generally called Infusorians. 



{Occurring in fresh and sea water ^ abundant in infusions.) 



9. FLAGELLATA, units with a definite rind, with 1-3 actively undu- 

 lating flagella, often with a distinct aperture for the entrance of food. 

 Reproduction by division into two, or by multiple division within a 

 cyst. Conjugation and encystation are common. Some forms are 

 colonial, and suggest the transition of Metazoa. 



