THE HIGHER ORGANISMS 



117 



So soon as it becomes clear that the purpose of cell 

 association is reproduction, and so soon as it can be 

 determined that among the associated cells some are 



FIG. 40. Volvox globator. A, the entire colony, surface view, showing the 

 biflagellate zooids and several daughter-colonies swimming freely in the interior; 

 the latter are produced by the repeated fission of non-flagellate reproductive 

 zooids (a). B, the same during sexual maturity, showing spermaries from 

 the surface (spy), in profile (spy') and after complete formation of sperms 

 (spy"); and ovaries from the surface (ovy, ovy", ovy'",) and in profile (ovy r ). 

 C, four zooids in optical section, showing cell wall, nucleus, contractile vacuole, 

 with adjacent pigment-spot, and flagella (ft). D'-D 5 , stages in the formation 

 of a colony by the repeated binary fission of an asexual reproductive zooid. E, 

 a ripe spermary. F, a single sperm, showing pigment-spot (pg) and flagella 

 (ft). G, an ovary containing a single ovum surrounded by several sperms. 

 H, oospenn enclosed in its spinose cell wall. (After Kirchner; B-H after 

 Cohn.) 



destined to perform the reproductive function alone, 

 the advantage of the association becomes clear for the 

 reproductive cells may then be relieved of other func- 

 tions through the vicarious activity of the other cells. 



