the mass. L. dasyphylla presents a third modification, the antheridium being a sac, and the dart-like groups of cells being ejected from the minute terminal orifice. The moving particles produced in the cells of these three forms, differ a little in shape, and as they do not germinate they are believed to be spermatozoids, though no cilia have been found on them. The Rhodomelaceæ, the last and highest family of florid Algæ, are, as the name implies, of a rich red brown colour. None of the other Rhodosperms can vie with them in peculiarity or variety of structure. The fronds may be areolate or reticulate, filiform or variously leafy, articulate or inarticulate. [Illustration: Fig. 27. Dictyurus purpurascens.] Some genera, as for example Dasya, have slender, often elegantly branched threads, while such genera as Amansia and Odonthalia have instead a flat and pinnatifid frond. The latter, which has a very conspicuous cellular reticulation, is a genus of high latitudes, but is common on some parts of the Scotch and North American coasts. The British seas are rich in many genera of this order, and analogous forms occur in the southern hemisphere, where there are at least twenty-three genera. Many are remarkable for their singularity of structure: the Claudea for example, which is one of the most elegant of the Algæ, has a cancellated frond and is the ornament of warm seas; the Amansia and Leveillea which are distinguished by the beautiful reticulation of their fronds caused by large hexagonal cells; and the Dictyurus, in which the net forms a spiral web round the principal stem. Fig. 27 shows a portion of the network of Dictyurus purpurascens magnified. All the genera of this order possess free areolate hollow conceptacles perforated above, and containing nuclei, from the base of which short tufts of threads arise, each bearing a large obovate spore at its apex. The tetraspores are arranged in series either within the frond, or in distinct pod-like receptacles called stichidia. Fig. 28 shows the Polyzonia cuneifolia with its tetraspores arranged in rows in their pod-like stichidia, together with the areolated conceptacle and spores, all highly magnified. The antheridia differ in form in the different genera. In the Dasya they assume that of pods full of cells, in which the motile particles are generated; in the Rytiphlæa tinctoria the antheridia resemble those of the Dasya except in being elliptical, and in the Rytiphlæa pinastroides they are cellular bodies, without any investing membranes, clothed with delicate hairs.