Volvox and Associated Algae from Kimberley. 475 



look for the explanation of a phenomenon already observed elsewhere, 

 but as yet nowhere to such a marked extent as in these Kimberley 

 pools, namely, the sudden and complete disappearance of Volvox 

 which often occurs when the water reaches a certain degree of lowness, 

 usually about 4 inches in depth, but long before the pool is nearly 

 dry and while associated animal (mainly crustacean) and plant life 

 continues unabated for some days longer. This disappearance is not 

 heralded by any apparent falling off in numbers or development, but 

 comes with remarkable suddenness, often apparently at the height of 

 development of the strain. A very few colonies continue for a time, 

 but the majority disappear completely in the course of a few hours. 

 High temperature * alone does not seem sufficient explanation, nor 

 can the Crustacea be entirely to blame. 



To give an idea of the sequence of events it is necessary first to 

 describe briefly the nature of the fauna and flora of the pool, or rather, 

 of the plankton, as revealed by Mr. Power's collections ; the attached 

 algae, of which some at least certainly occur, were not collected. All 

 collecting was done with a small net swept through the surface layers 

 of the water, so that planktonic life alone, and at that only the larger 

 species, was collected. 



The fauna consisted almost entirely of crustaceans of various kinds, 

 Streptocephalids being particularly abundant. It would be interest- 

 ing to correlate the appearance and numbers of the various species 

 with those of the associated algae, but that is not possible here. In 

 addition, a few Protozoa were noted ; Rotifers were scarce as com- 

 pared with other Volvox inhabited pools, but in one collection a few 

 individuals of Proales parasita were found in colonies of F. Rousseletii. 

 The parasite never obtained a very great hold on the Volvox, however, 

 probably owing to the brief duration of the pools. 



As regards the flora, besides two species of Volvox in Pool I it con- 

 sisted almost entirely of colonial forms belonging to the Tetrasporales 

 or Protococcales, with some Eudorina, while in Pools II and III Volvox 

 only was found, two species in Pool II, one only in Pool III, the latter 

 being the form of V. Rousseletii which is common to all three pools. 

 In the case of the two latter pools, however, too few collectings could 

 be made to establish much beyond the fact of the occurrence in them 

 of certain forms of Volvox. 



* A similar phenomenon was observed on the Cape Flats in November 1931, 

 when such a sudden disappearance followed on a day of very great heat, when 

 the water (3-4 inches deep) in the pool reached a temperature of over 32 C. at 

 midday. 



