Volvox in South Africa. 607 



after fertilisation the oosphere rounds off completely, the connecting 

 strands disappear, the neck is withdrawn, and the oosphere lies 

 completely within the peripheral layer of the parent (fig. 8, D). 

 On the other hand, as yet there are no observations of the entry of 

 sperms into the egg (or rather oosphere) to confirm or refute the 

 justice of this expectation, while there is abundant evidence to sug- 

 gest that the sperm enters the hollow of the parent, and thence 

 penetrates the oosphere. 



The only two workers who describe male nuclei within the oosphere 

 are Overton (1889, pp. 245-246, t, iv, fig. 29) and C. Lander (1929, 

 p. 434, pi. xv, figs. 4-17), and in neither case is the evidence given 

 convincing, and it appears at least possible that in both cases what 

 the observer actually saw were binucleate oospheres such as those 

 described above and not sperms entering the oosphere, and this 

 for the following reasons : 



1. Overton, describing and figuring sperms, lays stress on the fact 

 that in V. globator the sperm nucleus contains no nucleolus (1889, 

 pp. 245-246, t. iv, fig. 29), yet in his drawing of a fertilised oosphere 

 (fig. 29) he shows the male nucleus as a body of diameter about 

 equal to a third that of the female nucleus, with a large well-defined 

 nucleolus. 



2. In Miss Lander's paper, again, whereas her drawing of a sperm 

 (fig. 11) shows it as possessing a very small nucleus with minute 

 nucleolus, the drawings showing the supposed male nucleus within 

 the oosphere depict it as much larger than the whole spermatozoid, 

 about two-thirds the size of the large female nucleus, and with a 

 nucleolus which is only a little smaller than that of the oosphere 

 (figs. 13-16). Here, too, it seems possible that she is figuring stages 

 in the division of an oosphere nucleus, and not a case of fertilisation. 

 Further, her drawing of the pore by which the sperm is said to gain 

 entrance to the lateral receptive spot is far from conclusive it has 

 very much the appearance of a tangential section of a sperm adpressed 

 to the oogonium wall. 



Careful search has been made for similar structures in both living 

 and sectioned material of these two African species, so far without 

 success ; two doubtful cases were found where the wall of the 

 oogonium in a corresponding position showed some unevenness, 

 but compared with the hundreds of healthy normal oogonia which 

 showed no trace of any such structures their value is negligible. 



These two authors may be quite correct in their observations on 

 fertilisation, but as yet, apart from the very common occurrence of 



