VOLVOX 51 



11. Make a drawing, 60 mm, in diameter, showing a male 

 colony in optical section. In such a drawing only a single ring 

 of somatic cells should be shown but all of the clusters of micro- 

 gametes should be drawn in outline. Detailed structure of 

 one cluster of microgametes in side view and another in surface 

 view should be brought out. 



12. The two kinds of female colonies are much alike in 

 structure. In them, the distance between two somatic cells is 

 usually not more than the diameter of a single somatic cell. 

 There is no reliable constant difference in the appearance of 

 either the somatic cells or of the macrogametes in the partheno- 

 genetic female colonies and the true sexual female colonies. 

 Observations upon living material have demonstrated that the 

 chief difference lies in the number of gametes. The sexual female 

 colonies of this species contain sixteen or more gametes while 

 female colonies containing twelve or fewer macrogametes are 

 parthenogenetic female colonies. 



13. Make a drawing of each kind of female colony showing 

 colony wall in optical section and showing in outline the total 

 number of macrogametes characteristic of each. Show at least 

 one macrogamete in detail. 



14. See demonstration of zygote and draw one, in optical 

 section, about 20 mm. in diameter. 



