Volvox in South Africa. 581 



that of Kuschakewitsch for V. tertius and F. aureus, as will be most 

 clearly seen by a comparison of his figures (1925, p. 399, g-k) with 

 those given by Janet (1923, Plate 18, fig. 104). Although the process 

 in these two species does not concern us directly here, it is interesting 

 when we come to consider inversion in the case of the sperm globoids 

 and germ colonies. Pascher's account (loc. cit., p. 457) is based on 

 Zimmermann's work. The subject has already been discussed else- 

 where (Pocock, p. 485) in connection with F. gigas and F. africanus. 



Inversion has been described in Eudorina and Gonium by 

 Hartmann (1921, p. 223). Subsequent observers have noted it not 

 only in all the regular colony forming members of the Volvocales 

 but also in other members, e.g. Haematococcus. Thus the phenomenon 

 of cell-division to form a hollow sphere followed by inversion is 

 characteristic of the Volvocales as a whole, showing progressive 

 advance in complexity throughout the group as the number of 

 constituent cells in the colony increases, and culminating in the 

 species of Volvox of the Eu-Volvox section, of which F. Rousseletii 

 and F. capensis are members. The known facts are ably sum- 

 marised by Pascher (1927, p. 457) in so far as concerns the asexually 

 formed daughters. Logically, one is led to expect the same sequence 

 of events wherever in any member of the group a single cell divides 

 to form a spherical mass of cells, i.e. in Volvox in the development 

 of the sperm bundles and in the colony formed from the oospore. 

 The present investigation shows this expectation to be justified in 

 both cases. 



Powers describes the process as the "imagination and final in- 

 version" of the young colonies (1908, p. 141); Kuschakewitsch (1931, 

 p. 328) makes a similar use of the term invagination in describing 

 the first half of the process, and later in his discussion (p. 331) on 

 the significance of his discovery he considers the development of 

 the daughter colony from the gonidium to be a sort of internal 

 budding comparable to the invagination of a part of the wall of the 

 parent colony. The term has, unhappily, been used to describe the 

 whole process of re-orientation by subsequent workers in America, 

 either misunderstanding the use of the term made by these writers 

 or misled by a superficial resemblance at an early stage of the pro- 

 cess to the invagination of the blastula in animal embryology, e.g. 

 that of Amphioxus (Dendy, 1914, p. 47, fig. 13). But, whereas 

 there the essential part of the process is the infolding of one hemi- 

 sphere against the other to form a double wall, the cells of the two 

 layers of the wall being inversely orientated, in Volvox, although 



