GENERAL ZOOLOGICAL INTEREST. 



123 



considerable 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. 



FIG. 55. A colonial flagellate Infusorian Proterospongia 

 haeckelii. After Saville Kent. 



There are about 40 flagellate individuals, a, nucleus ; b, contractile 

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

 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. 



