476 Annals of the South African Museum. 



The common Volvox is undoubtedly very near to F. Rousseletii 

 West ; but since, as mentioned above, certain marked characteristics 

 distinguish it from the typical form, it is described here as a form of 

 that species to which the distinguishing regional name Griquaensis 

 is applied. It develops very quickly and is associated in Pool I with 

 a second species much slower in development. The young colonies 

 of the latter were frequent in the third collecting and somewhat 

 suggested F. africanus in appearance ; but whereas F. Rousseletii was 

 already in an advanced sexual phase this second species was obviously 

 still very young, with numerous large but still undivided gonidia. 

 In succeeding phases it never appeared in the first collectings. In 

 the first phase the pool dried up before any further stages could be 

 obtained, but, when next formed, the pool had a longer existence and 

 more advanced stages of the species were obtained in the later collec- 

 tions. These proved truly startling F. Rousseletii, previously 

 regarded as an unusually large species of Volvox, was completely 

 dwarfed by the maturing asexual colonies of the new species ; the 

 diameter of most of the colonies containing embryo colonies was well 

 over 2 mm., while colonies of 3 mm. or over were not unusual. The 

 first microphotograph (Plate XXV, A) shows the relative sizes well ; 

 in the centre are an average-sized male colony and an immature 

 asexual one of F. Rousseletii forma griquaensis, with a young colony, 

 such as was first observed, of the giant, and round these are four 

 maturing colonies of the latter, with fully formed daughters and 

 undivided gonidia. The group, as in the case of the other low-power 

 photographs reproduced, was floating in water in a glass dish and not 

 compressed by its own weight on a slide. When placed on the slide 

 such colonies flatten out enormously, appearing among associated 

 F. Rousseletii colonies as large, clear, nearly colourless circular 

 patches. 



It is considered that the name Volvox gigas can with justice be 

 given to this magnificent species.* No trace of sexual organs could 

 be found in this material nor in the succeeding collection during this 

 phase of the pool's existence ; but during the next phase, from the 

 third collecting onward, Volvox gigas became more and more abundant 

 until on 16th March it was the dominant organism among the plants, 

 showing all stages in sexual reproduction. Thus by repeated collec- 

 tions made at frequent intervals very rich material has been obtained 

 and consequently as full a description can be given as is perhaps 



* A specific name in honour of its collector was barred by the previous existence 

 of Volvox Powersii (=JBesseyosphaera Powersi Shaw), Printz. See p. 492. 



