Volvox in South Africa. 633 



may be sunk as regional forms or even as phases in the life-cycle of 

 other pre-existing species. 



Most emphatically study of preserved material of one or two small 

 collectings and those incomplete as regards the various reproductive 

 cells, without corroborative studies of living material, is in general 

 insufficient for creating new species ; existing descriptions based on 

 such material are, as a rule, extraordinarily lacking in important 

 details. 



SUMMARY. 



Two species of Volvox, V . Rousseletii G. S. West and V. capensis 

 Rich and Pocock, have been studied in the life, living as far as possible 

 under natural conditions, the former in tub and pond cultures at 

 Sea Point, the latter in its natural habitat on the Cape Flats. Both 

 are very closely allied to V. globator as regards cell-structure and life- 

 history. 



The vegetative cells are normally far more numerous than in that 

 species, are similar in structure, but differ in the shape of the chloro- 

 plast from the descriptions given of V. globator. Throughout the life- 

 cycle of a given strain there is great variation in both the number 

 and the form of the constituent cells. 



Asexual reproduction follows the same general lines as in V. globator. 

 The changes preparatory to inversion are described for the first time. 

 Inversion of the daughter colony is similar to the description of the 

 process in that species, but the connections between daughter and 

 parent are attached in a ring some distance from the edge of the 

 phialopore and not to the cells immediately round it. The phialopore 

 closes completely after inversion. The inverted daughter develops 

 within the much enlarged gonidium vesicle, never free within the 

 hollow of the parent. When mature, each daughter escapes outwards, 

 forming its own pore of escape. Liberation inwards was only once 

 observed and was probably pathological. 



Sexual Reproduction. T'. capensis is monoecious, V. Rousseletii 

 dioecious. In the former the colony produces 4 to 22 sperm globoids 

 and 60 to 150 oospores, and is strongly protandrous. In the latter 

 the male colony produces from 100 to several hundred sperm bundles, 

 the female 150 to 200 or more oospores. 



The male initial cell in V. Rousseletii in general shows a shifting 



of the polar axis of the cell before division, the phialopore of the 



sperm globoid being consequently directed sideways or inwards 



during development. In V. capensis there is no such shifting of the 



VOL. xvi, PART 3. 41 



