Observations on the Genus Volrox in Africa. 455 



The vegetative cell is similar in structure to that of V. capensis. 

 Plate XIX, fig. A, shows the appearance of cells at the anterior pole 

 of a mature colony (i.e. one with nearly mature daughters). The 

 position of the eyespot relative to the pole is well seen. The outer 

 membrane shows clearly, the inner only faintly. These cells were 

 living, the outer portions of the cilia lashing vigorously, and appear- 

 ing as a blurred zone outside the limiting membrane ; the basal 

 quarter, which does not move, shows clearly, as does the mode 

 of insertion, the bases of the two cilia being wide apart from one 

 another. 



The four other microphotographs in this plate show the difference 

 in the arrangement of the cells at the anterior and posterior poles 

 of a colony, as seen in surface view. B and C are portions of a 

 young middle-aged colony treated with iodine. In B, the connecting 

 strands and cell walls show clearly ; in C, from near the posterior pole 

 the cells are closely packed, and several show contractile vacuoles ; 

 near the bottom is an undivided gonidium. D and E are from 

 an older colony, living and unstained, slightly more enlarged. The 

 protoplasts are further apart and are becoming smaller, particularly 

 in the posterior zone, fig. E, where many strands are seen to be 

 anastomosing, and several contractile vacuoles in diastole are visible. 

 The walls show faintly in D. Text-figs. 3, A-C, show the structure 

 of cells from the anterior and posterior poles in greater detail. 



The sexual colonies are dioecious, and the anterior region is free 

 from reproductive elements. The male colonies (Plate XX, fig. B) 

 are usually elongated, with numerous antheridia which develop at 

 varying rates. Thus any one coenobium may contain all stages, from 

 antheridial cells which are still in early stages of enlargement, up to 

 mature sperm globoids, and in addition may show gaps where sperm 

 globoids have formed and escaped. The colony shown in fig. B 

 illustrates this particularly well. The number of antheridia varies 

 from about 120 (probably more) to over 200. The sperm globoids are 

 even more depressed than in V. capensis, and slightly smaller, with 

 the 512 spermatozoids closely packed (Plate XXI, figs. A and B). In 

 general the male globoid escapes outwards, as in V. capensis, and 

 moves freely in the water for a time before the sperms escape. The 

 delicate surrounding vesicle is left when the globoid escapes, and 

 numerous empty vesicles can be seen in any male colony from which 

 globoids have been escaping. The spermatozoid (text-fig. 3, D) is 

 elongated, 10 to 13 /M long, 2 p wide, with thickened base sometimes 

 drawn out into a short point, has an elongated chloroplast with one 



