. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . - The formationof zoogonidia commences by the repeated division of the nucleus, the numerous 1 A similar condition exists in many genera of the Siphonocladiales, where the reticulatedchloroplast is really formed by a fusion of a number of small parietal plates, which may in somecases be quite separate. 216 Chlorococcineae nuclei remaining in a peripheral position. The cytoplasm and chloroplasts thenbecome aggregated around each nucleus, formi
. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . - The formationof zoogonidia commences by the repeated division of the nucleus, the numerous 1 A similar condition exists in many genera of the Siphonocladiales, where the reticulatedchloroplast is really formed by a fusion of a number of small parietal plates, which may in somecases be quite separate. 216 Chlorococcineae nuclei remaining in a peripheral position. The cytoplasm and chloroplasts thenbecome aggregated around each nucleus, forming bodies of a plano-convexcharacter which after division of the nucleus become constricted into two parts,each part forming a zoogonidium. Sometimes the development of motile repro-ductive cells is arrested, so that the divisions of the original protoplast result inthe formation of aplanospores (generally 16 in the mother-cell; Cleve, 98).. Fig. 142. Halosphsera riridis Scbmitz. 1 and 2, vegetative cells. 3, part of the peripheralplasma during the formation of zoogonidia ; chr, chloroplast; pi, cytoplasm ; k, , zoogonidium. (After Gran and Schmitz, from Oltmanns.) Halospheera viridis Schmitz is really an inhabitant of the warmer tem-perate seas, although in the Atlantic Ocean it is carried northwards by theGulf Stream. It is not unlikely that Splnrra Kerguelensis Karsten, describedfrom the Antarctic Ocean, and Pachysphwra pelagica Ostenfeld, from theN. Atlantic, are developmental stages of Halosphsera. Family Hydrodictyaceae. In this family of the ChlorococcineaB the plant-body consists of non-motileccenobia of ccenocytes, floating freely in the water. The ccenocytes, whichare of very varied external form, are disposed so as to form a flat plate inPediastrum and arranged in the manner of a net in Hydrodictyon. In thedisc-like ccenobium of Pediastrum, in which there may be more than 100ccenocytes, those of the ma
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