VOLVOX GLOBATOR 61 



tions, by means of the flagella, which lash the water in 

 concert and with a regularity of stroke that might well 

 be the envy of a University crew. Volvox aurea is 

 another species of the genus; it is smaller than V. glo- 

 bator, the number of cells varying from 200 to about 

 4,000. 



A notable feature of Volvox is the fact that certain 

 cells appear to be told ofT for special work. Thus, in 

 Gonium, as we have noticed, each cell of the colony is 

 capable of producing a daughter-colony, but out of the 

 thousands of cells in the Volvox colony only about eight 

 are allowed to engage in this asexual reproduction. 

 These few cells are generally in the hinder region of the 

 parent colony, and they soon display a tendency towards 

 their function. They grow larger than the ordinary 

 cells, and, as a result of repeated division, develop into 

 daughter-colonies, appearing as so many small spheres 

 within the parent sphere. They ultimately rupture the 

 wall of the latter, escape, and grow to adult size. 



Special cells for sexual reproduction arise in certain 

 colonies. In their early stage they closely resemble 

 the cells told off for asexual increase as already described, 

 but they are more numerous. Later they become clearly 

 differentiated into male and female, the male being 

 called " androgonidia " (Gr. aner, a man; gone, genera- 

 tion), the female gynogonidia (Gr. gyne, a female, and 

 gone). In Volvox globator there are from two to five 

 male cells and from twenty to forty female cells. The 

 female cell, while still in the wall of the colony, becomes 

 flask-shaped, but later it makes its way into the inside 

 of the colony and becomes a rounded egg-cell. Within 

 the male cell a bundle of yellow, spindle-shaped, flagel- 



