Volvox in South Africa. 611 



process continues at the bottom of the pool, whereas in V. Rousseletii 

 the ripening oospores are retained much longer in the parent colony, 

 which moves about among the others retaining its firm outline and 

 shape for a considerable period before disintegration finally takes 

 place. 



Very occasionally in V. capensis abnormal oospores with thick 

 smooth walls were seen in specially active material during unusually 

 hot weather (Plate XXXIX, F). 



Liberation of the Oospores. 



The method of liberation of the oospores is sharply contrasted with 

 that of either the sperm globoids or daughter colonies. In both the 

 latter the liberation was, as it were, a voluntary act on the part of the 

 young organ. The oospores, on the other hand, are entirely passive. 

 When the requisite degree of ripeness is reached the whole parent 

 colony disintegrates, sometimes very rapidly ; the protoplasts fall 

 apart and the membranes apparently dissolve. 



A single colony of I*, capensis which contained reddened oospores 

 had apparently reached the limit of its life, for when placed on the 

 slide it collapsed under its own weight and disintegrated, liberating 

 the oospores : it had not been killed nor fixed in any way, nor had it 

 had the pressure of a cover-slip on it. No similar case has been 

 observed in V. Rousseletii, but probably a similar breaking up takes 

 place there, although more slowly. 



There are several indications that the oospores have not reached 

 full maturity when this takes place, but continue to mature in the mud 

 at the bottom of the pool. The speed with which maturity is reached 

 appears to vary considerably, largely depending on external conditions, 

 of which temperature is certainly one of the most important. The 

 observations on a form of F. Rousseletii at Kimberley, already recorded 

 (Pocock, p. 499), show that there maturation is very rapid, sometimes 

 at any rate complete within two or three weeks. 



It is evident that the oospores are very efficiently protected and 

 able to retain their viability for a number of years. In 1928 Volvox 

 capensis was found in large quantities in shallow pools inside wattle 

 scrub near Dabchick Vlei ; the two succeeding winters were dry, and 

 no pools formed in this spot, but in 1931 one pool partly filled and 

 Volvox Juveniles promptly appeared. The pool soon dried up, 

 however, and no sexual colonies were found. In 1932 a very much 

 larger area of the thicket was inundated, far more than in 1928, and 



