474 Annals of the South African Museum. 



instructive to watch its development, and this was fortunately made 

 possible by having on the spot a keen and experienced collector in 

 the person of Mr. Power. 



When next visited, on the 22nd of December, the pool was com- 

 pletely dry, but this rainy season in the Kimberley district proved 

 to be a somewhat abnormally prolonged one, characterised by a 

 succession of distinct downpours separated from one another by 

 several weeks of dry, hot weather. Consequently the various pools 

 dried up completely and refilled several times during the summer. 

 During the succeeding three months (January to April 1932) Mr. 

 Power kept the first Volvox pool under frequent observation, visiting 

 it at intervals of two or three days whenever it contained water, and 

 the present paper is the result of his observations and collectings. 

 Although a very incomplete record of the seasonal history of the pool, 

 the results are instructive, especially when compared with the facts 

 known about the behaviour of Volvox in other areas, and are par- 

 ticularly noteworthy as illustrating the extraordinarily rapid develop- 

 ment of certain forms of Volvox in a region of intermittent summer 

 rainfall, and the much greater rapidity of development under identical 

 conditions found in some species than in others. 



Meanwhile search for Volvox was continued in other local pools 

 without success, until late in the season, when it was found in two 

 more small pools, called Pools II and III respectively in this paper. 

 All three pools are formed in quarries from which building material 

 has been removed, and are therefore probably of comparatively recent 

 origin. Pool I is in typical red Kimberley soil, a mixture of clay 

 and very fine-grained sand, drying very hard ; owing to the fineness 

 of the particles it forms a thick suspension in the water, which is 

 consequently opaque and of a deep reddish colour throughout the 

 existence of the pool very unlike the clear water characteristic of 

 Volvox vleis on the Cape Flats. In Pool II, on the other hand, the 

 water is clear, the sides and bottom of the pool being formed of broken 

 stone, while Pool III is of yet a third type, since it is in limestone tufa, 

 of which material the sides and bottom are composed. The water is 

 muddy and has a higher lime-content than usual in the district. 



A point which may possibly have some bearing on the behaviour 

 of Volvox during its life-cycle, namely the Hydrogen-ion concentration 

 of the water, has not so far been investigated. Keeping in mind the 

 high day temperature, the rapid evaporation of the water, and the 

 enormous quantity of animal life present, it is probable that the pH 

 alters considerably and rapidly, and it is perhaps to this that we must 



