120 PHYLUM PROTOZOA- -THE S/MTLEST ANIMALS. 



several colonial forms ; in these the individuals are united by 

 their extra-capsular protoplasm, but are all equivalent. In 

 Proterospongia the cells show considerable morphological 

 distinctiveness ; some are flagellate, some amoeboid, some 

 encysted and spore-forming. Again, in Volro\\ as we 

 noticed above, the cells of the colonies show a distinction 

 into nutritive and reproductive units. 



FlG. 53. A colonial flagellate Infusorian Prolerospongia 

 haeckelii. After Saville Kent. 



There are about 40 flagellate individuals, a., nucleus; /'., contractile 

 vacuole ; c., amoeboid unit in gelatinous matrix; d. , dis-ision 

 of an amoeboid unit ; e., flagellate units with collars contracted ; 

 f., hyaline outer membranes ; g., unit forming spores. 



Lastly, in their antithesis of passivity and activity, con- 

 structive and destructive preponderance, anabolism and 

 katabolism, the Protozoa illustrate the phases of the cell- 

 cycle, and so furnish a key to the variation of higher 

 animals. 



