The Mastigophora 157 



The following genera are included: Eudorina Ehrenberg (103, 206); Go7iium Miiller 

 (103, 206; Fig. 4. 31, D); Pandorina Bory (206; Fig. 4. 31, A); Platydorina Kofoid (154, 

 268; Fig. 4. 31, B, C); Pleodorina Shaw (206); Stephanoon Schewiakoff (206); Volvox 

 Linnaeus (259); Volvuima Playfair (95). 



Life-histories show basic similarities throughout the group, btit certain 

 genera are less specialized than others. In Gotiiiim, Pandorina, and 

 Platydorina, daughter colonies may be produced by any member of the 

 parental colony. This is not the case in certain other genera. Reproduc- 

 tion is limited to flagellates of the posterior four rows in Eudorina, to 



Fig. 4. 31. A. Patidorina morum (Miiller) Bory (after Smith); colonies 

 may reach 250^ in diameter. B, C. Platydorina caudata Kofoid; surface 

 view, x225; lateral view, x260 (after K.). D. Gonium pectorale Miiller; colo- 

 nies reach diameters of 60-70/^; diagrammatic. 



those in the posterior half of the colony in Pleodorina, and to a few 

 flagellates ("gonidia") in the posterior half of the Volvox colony. 



In development of a daughter colony, continued fission within the 

 original membrane produces a hollow spherical or hemispherical stage, 

 the plakea (Fig. 4. 32, C), in which the anterior ends of the flagellates 

 are directed centrally. Later development in Gonium pectorale (103) in- 

 volves a flattening of the plakea, and then further inversion, so that the 

 young colony becomes slightly convex on the anterior, or flagellated, 

 surface. In Platydorina (268) the plakea is a hollow sphere with a single 

 opening (phialopore). After the 32-cell stage is reached, inversion occurs 

 through the phialopore and the inverted daughter colony becomes a 

 hollow sphere (Fig. 4. 32, Q). Further development involves collapse of 



