FLAGELLATA 



129 



and small are capable, each with its like, of equal, undifferen- 

 tiated conjugation ; so that we have a differentiation of sex far 

 other than that of ordinary, binary sex. Uudorina, however, 

 has attained to " binary sex," for the female cells are the ordinary 

 vegetative cells, at most a little enlarged, and the male cells are 

 formed by ordinary cells producing a large flat colony of sixty-four 

 minute males or sperms. In some cases four cells at the apex 



Fig. 45. Pandorina morum. A, entire colony ; B, asexual reproduction, each zooid 



' dividing into a daughter-colony ; C, liberation of gametes ; D-F, three stages in 

 conjugation of gametes ; G, zygote ; H-K, development of zygote into a new colony. 

 (From Parker's Biology, after Goebel.) 



of a colony are spermogonia, producing each a brood of sperms, 

 while the rest are the oospheres. The transition to Volvox must 

 have arisen through the sterilisation of the majority of cells of 

 a colony for the better nutrition of the few that are destined 

 alone for reproduction. 



Volvox, as we have seen,' has attained a specialisation entirely 

 comparable to that of a Metazoon, where the segmentation of 

 the fertilised ovum results in two classes of cells : those destined 

 VOL. I ^^ 



