Volvox and Associated Algae from Kimberley. 491 



portions. The colourless beak ends in a blunt point, the cilia, usually 

 a little longer than the spermatozoid itself (14-19 /A), being inserted at 

 opposite sides of the apex and directed sideways and forwards, not 

 backwards as in the globator and aureus types ; in this respect they 

 resemble the spermatozoids of Eudorina elegans. At the point of 

 insertion is a refractive granule. At the apex of the chloroplast and 

 near the base of the beak is a small red eyespot and adjacent to it are 

 two contractile vacuoles. Most often only one vacuole could be 

 distinguished, hence their periodicity is probably more or less alter- 

 nating. The narrow posterior part may be prolonged into a delicate 

 point or it may be rounded ; probably the posterior process may be 

 withdrawn or prolonged at will during the movement of the sper- 

 matozoid, as is the case in Eudorina. From the contorted shape of 

 many of the spermatozoids the movement is evidently a combined 

 amoeboid and ciliary one. In addition to the normal spermatozoids 

 numerous long-drawn out, structureless ones, particularly common 

 in older colonies, had evidently died before the material was fixed 

 (Plate XXX, C). In developing and mature sperm bundles starch is 

 present, but none could be detected in the free spermatozoids. They 

 are rather longer than usual in Volvox. 



(2) The female reproductive cells develop directly into oospheres ; 

 at first these can be distinguished from neighbouring somatic cells 

 only by the presence of more numerous pyrenoids, but the size con- 

 tinues to increase and the cilia are soon lost ; mature oospheres 

 vary a good deal in size, and are practically spherical in shape. 

 Spermatozoids swarming round the oospheres are common (fig. 

 3, L, M). 



The oospores are comparatively small (31-44 p,), with smooth 

 fairly thick exospore, within which, when ripe, the protoplast, enclosed 

 in the delicate endospore, lies somewhat eccentrically (fig. 3, N; 

 Plate XXX, C). When ripe they are reddish gold in colour even 

 in preserved material the large colonies with ripe oospores glitter 

 with a golden sheen when viewed by reflected light. The number 

 per colony is large, certainly several hundred, but probably not so 

 great as the number of androgonidia in the male colonies. In mixed 

 colonies the number varies enormously. Purely female colonies are 

 in general smaller than the mixed ones, which attain nearly, if not 

 quite, as great a size as the purely asexual ones (Plate XXV, D). 



From the above description it will be obvious that Volvox gigas 

 is a very distinctive, if somewhat primitive, species. The only form 

 as yet recorded which approaches it is that described by Powers 



