618 Annals of the South African Museum. 



near the surface. The posterior half is slightly broader than the 

 anterior, the pole broadly rounded. The chromoplast is massive, 

 cup-shaped, and uniformly golden brown, except now and again at 

 the edge where patches of green may show. The large nucleus with 

 conspicuous round nucleolus rests in the hollow of the cup, approxi- 

 mately in the centre of the cell (fig. 9, A, B). 



The zoospore is enclosed in a delicate hyaline wall which is at first 

 closely adpressed to the protoplast (fig. 9, A), but soon enlarges to 

 form a loose cover comparable to the vesicle surrounding a develop- 

 ing gonidium (fig. 9, B). At the anterior end, attached to the beak, 

 which is very short and placed somewhat asymmetrically, are two 

 cilia which diverge widely, penetrating the wall at two spots well 

 apart from one another. Immediately after liberation the cilia are 

 short but gradually lengthen until they are about as long as the 

 zoospore. The whole organism is very like a large golden-brown 

 Chlamydomonas, but with a loose wall which, so far as could be made 

 out, is not connected to the protoplast by protoplasmic strands as in 

 Sphaerella (Haematococcus), nor is the chloroplast like those usual 

 in the latter genus. It is far more like the cup-shaped structure 

 characteristic of Chlamydomonas, while the wall is similar to that- 

 seen in several species of this genus (cf. C. angulosa Dill, Pascher, 1927, 

 pp. 231-232, C. pteromoniodes Chodat, loc. cit., p. 208). 



No eyespot could be detected, nor would one appear to be necessary, 

 always assuming the eyespot to be the light-perceptive organ, since 

 the work of the zoospore is primarily cell-division and not food- making, 

 as it contains in itself sufficient food reserve to carry it over this first 

 phase in its existence. Nothing, therefore, would be gained by the 

 zoospore moving towards the light. On the contrary, such action 

 on its part would probably increase the danger of destruction. So 

 far as could be determined throughout its existence as a free unicellular 

 organism and well into the period of division it moves about on the 

 floor of the pool in which it lives (in cultures on the surface of the slide), 

 its power of movement undoubtedly acting as a means of protection 

 against predatory animal organisms. 



Soon after liberation the zoospore measures about 30 x 40 /JL ; it 

 enlarges slightly as it ages an hour later the same zoospore measured 

 36 x 46 p. (i.e. in both cases, the protoplast, not including the loose 

 cell- wall). The enlargement appears to be due to a decrease in the 

 density of the protoplast, which becomes slightly lighter in colour, 

 particularly at the surface, where the green patches may begin to 

 extend. 



