. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . tly arranged that the whole ccenobium has a very firm and solid ccenobium of Volvox, like that of Pleodorina, has a definite polarity, andOvertoil (89) has pointed out that in V. aureus the stigma ( eyespot) ofeach cell lies on the side turned towards the anterior pole, probably in relationto the positive phototaxy of the coenobium. In Pandorina and Eudonnathe stigma is large in the anterior cells, smaller in the equatorial cells a
. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . tly arranged that the whole ccenobium has a very firm and solid ccenobium of Volvox, like that of Pleodorina, has a definite polarity, andOvertoil (89) has pointed out that in V. aureus the stigma ( eyespot) ofeach cell lies on the side turned towards the anterior pole, probably in relationto the positive phototaxy of the coenobium. In Pandorina and Eudonnathe stigma is large in the anterior cells, smaller in the equatorial cells andinvisible in the posterior cells (Conrad, 13). In the lower forms of the Volvocese, Gonium, Pandorina and Eudorina,reproduction takes place by the formation of a daughter-ccenobium fromevery cell of the mother-colony (figs. 103 F and 104 B). The daughter-coenobium is formed within the wall of the mother-cell, which swells upand becomes mucilaginous, and ultimately by its dissolution sets the youngcolony free. In the highest type, namely Volvox, only certain of the re-productive cells, often termed parthenogonidia, give rise to Fig. 106. Pleodorina ilUnoisensis Kofoid. A specimen from Madras, x 500. r/c, gouidial orreproductive cell; vc, vegetative cell. The arrow marks the direction of translocation. An intermediate condition is found in Pleodorina californica, in which theformation of daughter-colonies is restricted to certain purely reproductivecells located in one half of the colony; and in PI. ilUnoisensis there is asimilar but sometimes a much less obvious restriction of the reproductivecells. In Volvox the parthenogonidia vary from 1 to 24 (commonly 4 or 8)and are scattered irregularly among the somatic cells. In Platydorina theyoung daughter-colony is at first cup-shaped, but subsequently becomesflattened and twisted. The normal development in Volvox begins withthe enlargement of the mother-cell, followed by successive divisions into Volvocea?
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