. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . iral twist. In the genus Spirodinium then-are often two longitudinal flagella in place of the more normal solitary one. The protoplast is colourless, or, as in Cochlodinium archimedes, uniformlytinted: and in Poiichetia there are numerous red droplets in the peripheral 4—2 52 Peridiniex region. Vacuoles of considerable size may be present in the cytoplasm,through which branched protoplasmic threads pass to the peripheral partof the protoplast
. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . iral twist. In the genus Spirodinium then-are often two longitudinal flagella in place of the more normal solitary one. The protoplast is colourless, or, as in Cochlodinium archimedes, uniformlytinted: and in Poiichetia there are numerous red droplets in the peripheral 4—2 52 Peridiniex region. Vacuoles of considerable size may be present in the cytoplasm,through which branched protoplasmic threads pass to the peripheral partof the protoplast. The nucleus, which is of comparatively large size andsomewhat variable in shape, may be anterior in position (as in Gymnodiniumfitscum) or posterior (as in Hemidinium). The chromatin granules arescattered, and on division there is a primitive mitosis. A red pigment-spot is present in some forms, but wanting in the genus Pouchetia there is a lens-like body associated with the pigment-spot, and it is assumed that the concentration of light upon the pigment-spotby this body largely influences the orientation of the cell. Trichocyst-like. Fig. 37. Lateral view of Amphidinium sulcatum Kofoicl. ami/., amyloid body; clir., chromato-phore; ep., anterior part of cell in front of transverse furrow; , flagellar pore; /./.,longitudinal furrow; ?;., nucleus; , transverse furrow (with flagellum); vac., 740 (after Kofoid). structures occur in certain species of Gymnodinium and Spirodinium, some-times forming a more or less continuous peripheral zone. Some speciesof these genera throw out numerous threads of mucus, either just previous toentering the resting state or on the advent of unfavourable external con-ditions : these threads rapidly swell up and form a colourless gelatinousenvelope. The chromatophores are disc-shaped, rod-like, or band-like, and aremostly of a golden-brown colour, although Gymnodinium viride is green,G. seruginosum is blue-green,
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