VOLVOX 



183 



Eudorina, measuring from '2 to 7 mm. in diameter. The 

 wall of the sphere consists of a thick membranous envelope 

 in which numerous cells, each provided with its own cell- 

 envelope, are imbedded. There may be as many as 12,000 



Fig. 40. 



Volvox globator. A, A sexually ripe colony, showing microgametes 

 O > and macrogametes, O. , in various stages of development. 

 B, A portion of the edge of the colony highly magnified, showing 

 three flagellate cells united by protoplasmic threads, and a single 

 reproductive cell, rp. st, stigma ; cv. contractile vacuole. (After 

 Kolliker.) 



of these cells. They form a single layer, and when viewed 

 from the surface present the structure shown in fig. 40, A. 

 The cell-bodies do not fill their envelopes, but are separated 

 from them by a relatively considerable space, and every cell 



