580 Annals of the South African Museum. 



apparently the case. No mention of it can be found in the extensive 

 Volvox literature until Powers (1908, p. 158) recorded its occurrence 

 in his description of species of Volvox from Nebraska, and photographed 

 some of the stages. It struck him as most interesting, and he sought 

 for it successfully in most of the other species with which he worked. 

 Unfortunately, he was unable to watch the complete process in living 

 material, and as a consequence misinterpreted the sequence of events. 

 For example, his figure of the " kettle " stage shows an early, not a 

 late stage of the process. Further, in the absence of knowledge of 

 the cytology of Volvox, he failed to recognise the full interest and 

 importance of the phenomenon. As a result, Powers' discovery, 

 although it is referred to by both West (1916, p. 179) and Shaw (1922, 

 p. 109), failed to obtain the recognition it undoubtedly deserved. 

 His photographs are, nevertheless, excellent so far as they go, and 

 enable one to determine which type of inversion exists in the species 

 he figures. 



In 1921 Zimmermann (1923, pp. 584-585) worked at the cytology of 

 Volvox (chiefly V. aureus), and as a result realised that the orientation 

 of the cell constituents during cell-division, as compared with that 

 in the mature daughter colony, involved a complete inversion of every 

 cell. At the time he thought that this turning of the cell axis through 

 an angle of 180 took place in each individual cell, as did Merton 

 (1908, p. 470) in the case of Pleodorina illinoissensis. The following 

 year there was published a short paper by Kuschakewitsch (1922, 

 p. 131) describing observations actually made by him three years 

 previously, in the summer of 1919, which threw a flood of light on 

 the whole problem. From this it became apparent that no shifting 

 of the cell constituents takes place within the cell, but that when 

 cell-division is complete the whole hollow spheroid formed turns 

 inside out, thus reversing the orientation of the individual cells.* 



Zimmermann (1923, p. 584) published a very interesting critique 

 on this paper by Kuschakewitsch and subsequently investigated the 

 process in both V. aureus and V. globator, in the case of the latter 

 giving a series of photographs of successive stages of inversion. 

 His account of the process in V. aureus differs in certain points from 



* Unfortunately, this paper has not been procurable for reference ; both Janet 

 (1923, p. 127) and Zimmermann (1923, pp. 584-585) refer fairly fully to Kuschake- 

 witsch's work, and their accounts were at first followed for the details given 

 here. Quite recently, however, Kuschakewitsch's paper has been republished 

 in the Archiv fur Protistenkunde (Bd. 73, 1931, p. 324) and has therefore become 

 more accessible. 



