GENERAL ZOOLOGICAL INTEREST. 123 
considerabie morphological distinctiveness; some are 
flagellate, some amoeboid, some encysted and _ spore- 
forming. Again, in Volvox, as we noticed above, the cells 
of the colonies show a distinction into nutritive and repro- 
ductive units. 
Fic. 55.—A colonial flagellate Infusorian— Proterospongia 
haeckeliz.—After Saville Kent. 
There are about qo flagellate individuals. a, nucleus ; 4, contractile 
vacuole; c¢, amoeboid unit in gelatinous matrix ; 3 @, division 
‘ of an amoeboid unit; e, flagellate units with collars contracted ; 
J, 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. 
