LESS. XXIV 



VOLVOX 



269 



transparent mucilage. Each cell (c) has a nucleus, a con- 

 tractile vacuole, a large green chromatophore, a small red 

 pigment-spot like that of Euglena (p. 47) and two flagella. 

 The cells are surrounded by thick mucilaginous cell walls 

 which do not give the reaction of cellulose, but are probably 

 formed of an allied carbohydrate. By the combined move- 

 ment of all the flagella a rotating movement is given to the 

 entire colony. 



Asexual reproduction takes place by certain of the zooids 



^ 



S v-~A 



FIG. 66. 



Part of a Volvox-colony showing the structure in greater detail than 

 in Fig. 65 : s, spermaries ; o, ovaries. (After Lang.) 



which are not ciliated, undergoing a process very like the 

 segmentation of the hydroid egg (p. 248), dividing into 2, 4, 

 8, 1 6, &c. cells (A, a, and D 1 D 5 ), and so forming a daughter 

 colony which becomes detached and swims freely in the 

 interior of the parent colony (A), by the rupture of which it 

 is finally liberated. In sexual reproduction certain cells 

 enlarge and take on the characters of ovaries (B, ovy, ovy', 

 ovy", ovy'" , and Fig. 66, o) the protoplasm of each forming 



