104 



PROTOZOA. 



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

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

 no contractile vacuole. Reproduction Ijy 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 amceboid ; but, except in a very few case;, 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. — Moiwcyslis, in earthworm ; Gregarina, with a cross par- 

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

 stages, within a cell of the host ; Di-epanidiuin, and other forms, in blood 

 corpuscles ; Myxiduim, with amceboid adult ; Sarcocystis, in muscle 

 fibres of Mammals and some other Vertebrates ; Coccidhini oviforiiie, a 



Fig. 30. — A Colonial Flagellate Infusorian — Proterospongia 

 Ili-eckelii. (After Saville Kext.) 



There are about 40 flagellate individuals, a, nucleus ; l\ contractile 

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

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

 outer membranes ; g^ unit forming spores. 



])ermanent cell parasite, in many Vertebrates, common in the liver of 

 rabbits, &c. 



D. — Predominantly Active Forms (ciliate and flagellate), 

 generally called Tnfiisorians. 



(Oicun-iiig 11! fresh and sea water, ahiindaiit in infusions.) 

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

 lating flagella, often with a distinct a]ierture 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. • 



