Volvox in South Africa. 593 



4. Maturation of Sperm Globoid within the Parent. 



As soon as inversion is complete before the pore has quite closed 

 the globoid begins to move, rotating slowly with a rocking of the polar 

 axis, like a very flat top. The cilia are already long and soon attain 

 their full length (Plate XLIV, G). At first the central hollow is 

 broadly elliptical, but as development continues the globoid becomes 

 more and more flattened until in side view the hollow is almost 

 obliterated, appearing as a very narrow ellipse. The phialoporic 

 upper surface is convex, the lower more or less flattened. The 

 component cells are long and narrow with bluntly rounded ends, 

 the apices are clear, the inner two-thirds filled with the fairly dark 

 green chloroplasts, the line of demarcation between the outer colour- 

 less zone and the inner green zone being very clean cut (cf. Plate 

 XLIV, C, F). This contrast between the inner and outer zones is 

 very characteristic of recently inverted globoids, later becoming far 

 less well defined (fig. 6, K, L). 



Owing to the movement, photographs of living material cease to 

 be possible as soon as inversion is completed later stages have to be 

 obtained from material which has first been killed. After an hour 

 or two the globoid has reached its maximum depression, the chloro- 

 plast is more diffuse and lighter in colour, and the coloured zone is no 

 longer sharply differentiated from the colourless outer zone but passes 

 gradually into it. The component cells are more elongated, radiating 

 from the central hollow, with very long cilia, the arrangement of which 

 is very characteristic from the centre of the under side they radiate 

 out, those near the edge bending round it and upwards, while those of 

 the upper surface stretch up in the direction of the phialoporic pole 

 (fig. 6, L). Powers (1908, p. 164) gives an excellent description of the 

 appearance and movement of the mature sperm globoid in V. per- 

 globator which applies equally here. The pyrenoid in the base of the 

 cell is small, oval in outline, and the nucleus elongated ; the small 

 eyespots are sometimes visible. The cilia are very much longer in 

 proportion to the size of the cells than in the daughter colony (cf. 

 Plate XXI, A). Soon after inversion a delicate wall is laid down on 

 the outside ; traces of the beginning of this wall may be seen in 

 sections where the colourless ends of the sperms are edged with mucila- 

 ginous matter. So far as could be seen, no membranes separate 

 the sperms nor bound the central hollow. Even the outer wall is 

 very difficult to distinguish ; it only becomes clear as the sperms are 

 liberated. 



