20 



ANIMAL FORMS 



from place to place. As just indicated, some individuals 

 lack the flagella, and their subsequent careers show them 

 to be of a peculiar type. Sooner or later each undergoes 



a series of divisions form- 

 ing a little globe of cells, 

 which migrates into the in- 

 terior of the parent sphere 

 and develops into a new 

 colony. Within a short time 

 the walls of the parent 

 break, liberating the im- 

 prisoned young, which con- 

 tinue the existence of the 

 species while the parent or- 

 ganism soon decays. 



Under certain circum- 

 stances, instead of develop- 

 * n & c l n i es by such a meth- 



od ' some of the cells ma y 



store up food matters and 

 become eggs, while others, 

 known as sperm-cells, de- 

 velop a flagellum, and sep- 

 arating from the colony 

 swim actively in the sur- 

 rounding water, where each 

 finally unites with an egg. 

 This union, like that of the 

 two individuals in Vorticel- 

 la (Fig. 8, J, c), results in 



tne POWCr of division, and 



FIG. 10.-A, Volvox minor, entire colony 



(from Nature). B, C, and D, reproduc- the egg enters Upon its de- 

 tive cells of Volvox globator All highly i j . \ 



magnified. velopment, dividing again 



and again. The cells so pro- 



duced remain together, form a sphere, and finally develop 

 a Volvox colony. 



