606 Annals of the South African Museum. 



by Powers (1908, p. 164) in the case of V. pcrglobator is descriptive 

 and appropriate. 



Fertilisation. 



Unfortunately the behaviour of the sperms has not been observed 

 except immediately after liberation. No authentic case of sperm 

 attraction by oospheres has been seen nor any entry of sperms into 

 female colonies, although they have often been seen already inside 

 such colonies. Hence the act of fertilisation in Volvox still remains 

 a mystery. 



Sperms have been watched repeatedly inside both monoecious and 

 dioecious colonies (i.e. in both V. capensis and V. Rousseletii); in 

 many such cases the sperms were moving about and apparently 

 trying to effect an entrance through the vesicle wall (fig. 8, B, C). 

 This seems to be a very common state of things, as it was observed 

 in F. globator by many of the earlier workers, e.g. Cohn (1875, p. 104), 

 Klein (18896, pp. 35-36). But although many observers have 

 watched sperms inside the colony apparently swarming round young 

 oospheres, no one has as yet recorded the entrance of the sperm into 

 the oosphere in any such case (Mainx, 1929, p. 210). Klein mentions 

 that he frequently found dead sperms within colonies with ripening 

 oospores. 



A priori it seems contrary to expectation that sperms liberated 

 into the water should have to penetrate the massive parent colony, 

 and thus make their way to the back of the oosphere while all the 

 said oospheres have their anterior ends (where in general throughout 

 many groups of oogamous plants receptivity is localised) so near the 

 surface of the parent that penetration there must be at least as easy 

 as, probably much easier than, entry into the parent. Further, 

 subsequent to inversion of the colony the phialopore in general 

 closes completely, leaving no traceable pore which could serve as the 

 regular means of entry for the sperms, such as the "polar plateau" 

 described by Overton (1889, p. 243) in the case of V. aureus. It is 

 true that in F. capensis as in F. globator there are always the gaps 

 left by escaped sperm globoids, and that these gaps are always in the 

 midst of developing oospheres, yet they must be regarded as more 

 or less fortuitous, and, moreover, are generally closed on the inside by 

 the empty vesicle of the escaped globoid. 



From consideration of the structure of the colony and oosphere, 

 then, the expectation is that fertilisation should take place from the 

 outside, entry being effected at the apex of the oosphere. Moreover, 



