270 



THE EVOLUTION THEORY 



male. In the former the cells remain as they were before, but in the 

 male colonies the sixteen or thirty-two cells undergo a peculiar 

 process of division, which ends in each becoming a mass (16-32) of 

 so-called ' zoosperms,' that is, minute, narrow, longitudinally elongated 

 cells with two flagella (Fig. 63 at i) shows those of Volvox). In 

 Eudorina they differ from the female germ-cells or ova externally in 



MkifJ 1 



Fig. 63. Volvox aureus, after Klein and Sehenck. 

 A, besides the small flagellate somatic cells of the colony 

 there are five large egg-cells (t) which are capable of 

 parthenogenetic development, three recently fertilized egg- 

 cells (0) and a number of male germ-cells (a) in process of 

 multiplication. From each of these, by continued division, 

 a bundle of spermatozoa arises. B, a bundle of thirty-two 

 sperm-cells in process of development, seen from above. 

 G, the same seen from the side. Magnified 687 times. • 

 D, individual spermatozoa, magnified 824 times. 



form and size, as well as by being much more actively motile, and 

 they contain green and subsequently yellow colouring matter, and 

 a red eye-spot. We here find, for the first time among multicellular 

 organisms, the differentiation of male and female germ-cells ; and we 

 learn from this that the essence of fertilization does not lie in this 



