500 Annals of the South African Museum. 



The most striking characteristic of the form, however, is the great 

 rapidity of development ; this is brought out clearly in the field 

 notes given below (p. 509), but the most marked and at the same time 

 most complete record may be summarised here : 



The pool had dried up completely by 24th February 1932. Three 

 days later heavy thunder-showers during the night of Saturday, 

 27th February, filled the pool once more. The following Wednesday 

 (2nd March) a fine crop of Juveniles, with a few very young second- 

 or third-generation colonies, was obtained. Two days later (i.e. in 

 less than a week after the rain) among large asexual colonies containing 

 up to 10 embryos were a number of sexual colonies, mostly young 

 (Plate XXXIV, A), while by 7th March it had reached the height of 

 the sexual phase, and a week later had almost disappeared, although 

 the pool did not dry up until some time later. 



Obviously it is a form well adapted to the local conditions, which 

 are such that any pools formed can have only a short existence, 

 although they may form several times during a single season. From 

 observations made on the Cape Flats during last year one is forced 

 to the conclusion that a relatively high temperature is beneficial to 

 both the rate and degree of development, provided the water does 

 not fall below a certain depth. 



The behaviour of Volvox in the neighbourhood of Kimberley is 

 very suggestive of the notes made by Powers (1908, p. 141) in Nebraska, 

 where conditions appear to be very similar to those prevailing in some 

 parts of Africa where there is a summer rainfall. 



V. Rousseletii was found in all stages in Pool I each time it filled, 

 and after the last rainfall in asexual stages only in Pools II and III. 

 The identification of the latter is therefore only provisional ; at 

 present, however, there is no reason to regard the latter material as 

 at all distinct from that from Pool I. Other pools in the neighbour- 

 hood were examined for Volvox but so far without success. 



