[Illustration: Fig. 158. Portion of thallus of Coleochæte scutata, showing four antheridia formed from one thallus cell; a single spermatozoid at the right. (After Pringsheim.)] =324. Fruiting stage of coleochæte.=—It is possible at some seasons of the year to find rounded masses of cells situated near the margin of this green disk. These have developed from a fertilized egg which remained attached to the plant, and probably by this time the parent plant has lost its color. =325. Zoospore stage.=—This mass of tissue does not develop directly into the circular green disk, but each of the cells forms a zoospore. Here then, as in œdogonium, we have another stage of the plant interpolated between the fertilized egg and that stage of the plant which bears the gametes. But in coleochæte we have a distinct advance in this stage upon what is present in œdogonium, for in coleochæte the fertilized egg develops first into a several-celled mass of tissue before the zoospores are formed, while in œdogonium only four zoospores are formed directly from the egg. =326. Asexual reproduction.=—In asexual reproduction any of the green cells on the plant may form zoogonida. The contents of a cell round off and form a single zoogonidium which has two cilia at the smaller end of the oval body, fig. 157. After swimming around for a time they come to rest, germinate, and produce another plant. =327. Sexual reproduction.—Oogonium.=—The oogonium is formed by the enlargement of a cell at the end of one of the threads, and then the end of the cell elongates into a slender tube which opens at the end to form a channel through which the spermatozoid may pass down to the egg. The egg is formed of the contents of the cell (fig. 159). Several oogonia are formed on one plant, and in such a plant as C. scutata they are formed in a ring near the margin of the disk. [Illustration: Fig. 159. Coleochæte soluta; at left branch bearing oogonium (_oog_); antheridia (_ant_); egg in oogonium and surrounded by enveloping threads; at center three antheridia open, and one spermatozoid; at right sporocarp, mature egg inside sporocarp wall.] [Illustration: Fig. 160. Two sporocarps still surrounded by thallus. Thallus finally decays and sets sporocarp free.] [Illustration: Fig. 161. Sporocarp ruptured by growth of egg to form cell mass. Cells of this sporophyte forming zoospores. Figs. 160, 161. C. scutata.] =328. Antheridia.=—In C. scutata certain of the cells of the plant divide into four smaller cells, and each one of these becomes an antheridium. In C. soluta the antheridia grow out from the end of terminal cells in the form of short flasks, sometimes four in number or less (fig. 159). A single spermatozoid is formed from the contents. It is oval and possesses two long cilia. After swimming around it passes down the tube of the oogonium and fertilizes the egg.