PLEODORINA AND VOLVOX 



197 



been described (Fig. 26, B), typically consisting of 128 

 cells, of which only about one-half, situated in the 

 hinder part of the ccenobium, are capable of division, 

 while the remaining cells in the front part of the 



FIG. 27. Volvox aureus. x 180. (After Klein.) A ccenobium which has 

 produced all three kinds of germ cells. The three large (walled) 

 spherical cells are fertilised eggs, the small groups of cells are 

 derived from androgonidia, which will divide further to form 

 sperms (cf. Fig. 28, D), the largest spheres are young ccenobia 

 derived from parthenogonidia ; division in these last is complete, 

 but the cells have not yet separated. Note that about a quarter 

 of the mother crenobium (the front quarter) is free from repro- 

 ductive cells. The arrow shows direction of locomotion. Compare 

 Fig. 26, A and B. 



ccenobium are somatic, i.e. sterile and incapable of 

 division. This marks a further step in the restriction 

 of the reproductive (germ) cells. 



Volvox. In Volvox, the largest and most highly 

 differentiated member of this series of forms, the 

 ccenobium consisting of many hundreds of cells, the 



