Volvox in South Africa. 561 



while some are already well developed, others, particularly the male 

 cells, remain small till much later. It could not be determined whether 

 in this species the reproductive cells are differentiated before inver- 

 sion or immediately subsequent thereto. In a few cases inverting 

 daughters showed cells rather larger than the majority, but in most 

 cases no difference between the component cells could be detected 

 before inversion (cf. Plate XLI, G, H). Very soon after completion 

 of inversion, however, they become conspicuous. 



In V. capensis, from the Cape Flats, on the other hand, abundant 

 evidence was forthcoming to show that the reproductive cells are differ- 

 entiated before inversion and before the last cell division (fig. 1, E, F ; 

 Plate XLI, A). The inference seems inevitable that here, at any rate, 

 the reproductive cells are cytologically equivalent to at least two 

 vegetative cells, possibly more ; this is also suggested by the larger 

 number of protoplasmic connections between the gonidia and the 

 neighbouring somatic cells. 



In both species no division of the reproductive cells takes place 

 until some considerable time subsequent to birth ; during the inter- 

 vening period the only visible changes which take place in them are 

 further increase in size and in the number of pyrenoids and, later, 

 loss of the cilia. The sexual reproductive initials are smaller than 

 the asexual at birth, and show great variation in size in one colony, 

 particularly in the case of the male. 



Types of Reproductive Cells and their Distribution. The three types 

 of reproductive cells are at first similar to one another in structure 

 and appearance, but are distinguished by their subsequent behaviour : 



1. The Gonidium, by repeated division, gives rise to a daughter 

 colony similar to the parent. 



2. The Male Initial Cell, Antheridium Mother-cell, or Androgonidium 

 by a similar method gives rise to the sperm globoid. 



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

 produces a single large oosphere. 



The terms Androgonidium and Gynogonidium were introduced by 

 early workers and have been very generally used subsequently. 

 They are convenient terms by which to describe the large cells which 

 eventually give rise to the male and female gametes, but since their 

 use is controversial they are avoided here. The homologies of the 

 various reproductive cells are discussed later. 



In V. Rousseletii the three types of reproductive cells are in general 

 found in separate colonies, while in V. capensis male and female cells 

 are formed in the same colony, the former always in much smaller 



