Volvox in South Africa. 605 



of these phenomena are possible the former may quite conceivably 

 be cases of parthenogenetic development in situ of unfertilised oospheres 

 such as is recorded by Overtoil (1889, p. 32) and Klein (1890, p. 23), 

 while the latter may be fertilised eggs in which fusion of the male 

 and female nuclei has been delayed. 



Other workers for example, Cohn (1875, p. 170), Overton (1889, 

 p. 245), Zimmermann (1921, p. 275), and Fritsch (1927, p. 81, and 

 MS.) take a different view of the homologies of the reproductive 

 cells. Although similar in origin they do not consider them homolo- 

 gous to the gonidium, since the ultimate products of their develop- 

 ment are different. These workers regard the male and female 

 initial cells as the mother-cells of the antheridiurn and oogonium 

 respectively, the contents of the former dividing repeatedly to form 

 the sperm bundle, while the latter, without division, forms an oogonium 

 containing a single large oosphere. In the latter case this view 

 presents no difficulty the Volvox oogonium is comparable with the 

 equivalent structures found elsewhere among the algae, where a 

 single cell becomes more or less flask-shaped and the contents, 

 enormously enlarged with food reserve, after union with a male 

 gamete clothe themselves with a several-layered wall and form a 

 zygote. In the case of the " antheridium," however, the matter is 

 not so simple, since here not only do the contents of the mother-cell 

 divide repeatedly, but the mass of cells so formed undergoes very 

 complicated developmental processes, at the end of which it clothes 

 itself with a delicate wall, escapes from the parent, and for a time 

 leads an independent existence. If, therefore, this view is accepted, 

 we have under consideration an antheridium of quite exceptional 

 type differing in several ways from all other antheridia. As, however, 

 the forms included under the general name Volvox constitute a very 

 highly specialised group, standing in many ways by itself as the 

 culminating point of one line of evolution, and showing several 

 characteristics which are found nowhere else among plants, notably 

 the formation of asexual reproductive cells (gonidia) which develop 

 in situ to form embryo colonies, it is not surprising if they also show 

 peculiarities in the formation of their sexual organs. 



Accepting the latter interpretation, then, the whole structure 

 derived from the initial cell, including the much enlarged wall or 

 vesicle, constitutes a highly specialised antheridium in which the 

 contents form a mass of spermatozoids, the sperm bundle ; this for 

 a time acts as a unit, and as such leads an independent life. In 

 the species of the Eu-Volvox section the term " globoid " suggested 



