. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . r mostly during the night, but only under favourable conditions, andgenerally while the organisms are motile. The plane of division is longi-tudinal in Phalacroma, and obliquely longitudinal in many genera, suchas Ceratium. The nucleus first divides, the parallel threads (vide page 64)dividing across the middle, whereupon the whole nucleus constricts into twohalves, each of which becomes rounded. In Ceratium, division of the wholeprotoplast f
. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . r mostly during the night, but only under favourable conditions, andgenerally while the organisms are motile. The plane of division is longi-tudinal in Phalacroma, and obliquely longitudinal in many genera, suchas Ceratium. The nucleus first divides, the parallel threads (vide page 64)dividing across the middle, whereupon the whole nucleus constricts into twohalves, each of which becomes rounded. In Ceratium, division of the wholeprotoplast follows immediately after the division of the nucleus, and then thehard cell-wall begins to separate into two pieces along certain of the existingsutures between the plates. Lauterborn (95) first described this line ofseparation in Ceratium hirundinella, but Kofoid (07 c and D) has given amuch better account of the fission-plane in a number of other species of thegenus (figs. 43 and 49). Starting from the ventral area in the apical half of the cell, the line offission passes between 4 and 4, 4 and 3, 3 and 3, 3 and 2, 3 and 2; then PeridiniacesB 69. across the girdle into the antapical half between 4 and 3, 3 and 2 2 and 2, 2 and 1, V and 1, and so back again to the ventral area (see fig. 49). The so-called ventral plate, which forms the ventral area, is thus obliquely divided by the fission-plane into an anterior and a posterior portion. The position of the fission-plane with reference to the skeletal plates was correctly given by both Blitschli (85) and Bergh (86), but only Kofoid (07 c and D) has given a complete and correct account of the number and disposition of the plates. As the daughter-cells separate after thedivision is completed, their exposed proto-plasmic surfaces become so moulded as tocomplete the normal outward form of the are at the same time clothed with a thinwall which soon shows the plates and suturescharacteristic of the species. In Per
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