50 



PROTOCOCCOIDEjE. 



has at first a large colourless anterior end, 4 cilia, and 2 " eye- 

 spots" (Fig. 45 G), but these soon disappear and the cell becomes 

 uniformly dark-green and spherical, and surrounds itself with a 

 thick cell-wall, losing at the same time its power of motion : the 

 zygote (Fig. 45 H) is formed, and becomes later on a deep red 

 colour. On the germination of the zygote, the protoplasmic cell- 

 contents burst open the wall (Fig. 45 J), and emerge as a large 

 swarmspore (Fig. 45 K) which divides into 16 cells, and the first 

 small individual is formed (Fig. 45 i, M). 



Eudorina is like Pandorina in structure, but stands somewhat 



FIG. 46. Volvox gfobator, sexual individual : a antheridia which have formed sperniato- 

 zoids ; b oogonia. 



higher, since the contrast between the conjugating sexual cells is 

 greater, the female one being a motionless oosphere. 



The highest stage of development is found in Volvox (Fig. 46). 

 The cells are here arranged on the circumference of a sphere, and 

 enclose a cavity filled with mucilage. The number of these cells 

 may vary from 200-22,000, of which the majority are vegetative 

 and not reproductive, but some become large, motionless oospheres 

 (Fig. 46 b) ; others, which may appear as solitary individuals, 

 divide and form disc- shaped masses of from 8-256 small spermato- 



