Volvox and Associated Algae from Kimberley. 477 



possible from the examination of preserved material only. Observa- 

 tion of living material is of course needed to fill in details of habit and 

 general behaviour, such as reaction to light, and of some phases of 

 development, as, for instance, certain stages in the development of 

 the embryo colonies, and the mode of escape on maturity. As 

 regards response to light, since the eyespots in the anterior part of 

 the colony are particularly large and well developed, there is no doubt 

 that this species, like the other members of the Volvocinae, is strongly 

 phototactic. 



Soon after the appearance of young colonies of Volvox gigas in the 

 pool non-motile gelatinous colonial algae begin to be prominent in 

 the phytoplankton. As development in the pool proceeds and the 

 water grows lower, these increase enormously in amount, while the 

 Volvox decreases, until finally it disappears altogether and the flora 

 is composed entirely of these gelatinous forms. Thus during the 

 existence of the pool there are several distinct stages, each character- 

 ised by the appearance or dominance of a different alga or group of 

 algae : first, Volvox Rousseletii develops in enormous quantities, then 

 Volvox gigas appears, and sometimes, but not always, becomes domin- 

 ant ; about the same time the other colonial algae begin to get 

 numerous, subsequently increasing greatly, until finally they alone 

 survive. 



These colonial algae included at least four different forms, all of 

 which at first appeared to belong to different genera. On further 

 examination, however, three proved to be forms of one extremely 

 polymorphic species which has been identified as belonging to the 

 genus Sphaerocystis Chodat (1897, p. 119). In its first mature form 

 this is a striking and very beautiful alga, very unlike anything hitherto 

 seen (Plate XXXVI, B). The colony is usually an almost perfect 

 sphere with 16 or 32 (occasionally 8) ellipsoidal groups of large green 

 spherical cells placed symmetrically within the periphery of the 

 sphere. The regularity of the arrangement of these groups within 

 the common envelope, the uniformity of the number and size of the 

 cells composing the groups in any one colony, and their symmetrical 

 spacing distinguish it from anything as yet described (Chodat, 18976, 

 p. 293, emphasises the irregularity often seen in his species, Sph. 

 Schroeteri), and it is therefore regarded as a new species to which the 

 name Sphaerocystis Poweri, in honour of its collector, is given (Plates 

 XXXVI and XXXVII.) 



But in addition to this striking spherical form other forms appear, 

 and, since there are transition stages present, all evidently belong to 



