Volvox in South Africa. 601 



may have something to do with this difference in the rate of in- 

 version. As far as could be made out, the number of sperms forming 

 the globoid is the same in the two species, so that difference in 

 number is not the cause of the difference in rate of inversion. 



(3) The mature globoid is similar in size and appearance to that 

 of F. Rousseletii, except that, as a rule, it is not quite so much 

 depressed, and the central hollow as a consequence is wider as seen 

 in side view, and, further, the sperms appear to be somewhat less 

 tightly packed (cf. Plate XV, C, D, and Plate XXI, A, B). 



In one case accidental crushing of a sperm globoid directly after 

 inversion resulted in the partial separation of the constituent cells, 

 the structure of which was thus well seen (cf. fig. 7, A). The outline is 

 oblong, ends truncate, slightly rounded, cilia inserted to one side of 

 the anterior end, eyespot and nucleus near the clear end, the massive, 

 slightly oblique chloroplast with pyrenoicl filling up the posterior 

 two-thirds. As the globoid ages, the form of the component cells 

 gradually approximates to that of the mature sperms. In a mature 

 globoid, 42 fj, in diameter, the central hollow seen in optical equatorial 

 section measured 20 p, the sperm cells 10 p, after liberation the sperms 

 are longer by the length of the beak, 2-3 /JL while the nucleus is placed 

 centrally. 



C. The Female Initial Cell Oogonium Mother-cell, or Gynogonidium. 



1. Enlargement. The very young female initial cell (fig. 8, A) is 

 similar to the gonidium and male initial at the same stage. But 

 very early in development, while still ciliate, it becomes distinguished 

 from them by the deepening of its colour to a strong dark green. 

 This shows well in the photograph of portions of a male and a female 

 colony of V. Rousseletii lying side by side (Plate XXXIX, E). In 

 the female colony are several mature oospheres seen in surface view 

 and a younger one in side view, with its apex very near the outer 

 membrane, while in the male colony are two young undivided 

 antheridium mother-cells, one seen side view, the other surface, 

 showing the nucleolus, and a mature sperm globoid in surface 

 view. 



As the oosphere enlarges (fig. 8, B, C), the posterior portion 

 projects further into the hollow of the parent, the apex remains 

 near the surface, and the whole in general becomes distinctly 

 flask-shaped (Plate XXI, D), though the shape varies a good deal. 

 The neck of the flask is sometimes very much shorter and broader 

 than the one here shown. In general, in F. Rousseletii the oosphere 

 VOL. xvi, PART 3. 39 



