Text-Fig. 3.—Oogonia of C. maschalocarpum showing the final stages of maturation. A—An eight nucleate oogonium still within the conceptacle as in 2D, but with the eight nuclei peripherally arranged. Built up from 12 consecutive sections. B—An eight nucleate oogonium after extrusion, but before degeneration of the supernumerary nuclei. Built up from 16 consecutive sections. C—An eight nucleate oogonium after extrusion, but with seven nuclei degenerating, and with the one functional nucleus in a peripheral position. Built up from 24 consecutive sections. The numbers indicate the level of the section in which that nucleus appeared. Scale = × 275. and S. tortile, or whether fertilisation took place whilst the nucleus was in a peripheral position or whether it first migrated to the centre. No four-nucleate oogonia were found, nor any stages in nuclear division. This may be due to the limited time range over which fixations were made —i.e., from approximately 8.30 a.m. until 11.30 a.m.—as Abe (1938) found that nuclear division in Sargassum tortile commenced during the afternoon and was completed by the following morning when extrusion took place. Extrusion and Embryology In all four species, the liberated oogonium contents are not released free into the sea but remain attached to the receptacle by a firm, mucilaginous stalk formed from the oogonium wall. In this position fertilisation takes place and sporeling development commences. Dawson described sporelings with a tuft of sixteen rhizoids in C. flexuosum, and Delf described well developed sporelings but was unable to assign them to a species. In the present investigation sporeling development was followed from attached sporelings in the three species in which they were found—that is, in all except C. elongatum. The first median wall (Text-fig. 4A) dividing the sporeling into two multinucleate portions was seen only in C. plumosum, but the following stages were found in all three species. A protuberance next developed at one end and was cut off to form a relatively large, densely staining, multinucleate rhizoid initial (Text-fig. 4B), which soon divided longitudinally (Text-fig. 4C) to produce a basal tuft of sixteen rhizoids (Text-fig. 4J). Meanwhile subdivisions in the body of the sporeling had resulted in the formation of a small-celled surface layer enclosing a central region (Text-fig. 4F). In the most advanced of the attached sporelings, transverse sections showed about 16 peripheral cells surrounding 8 central ones (Text-figs. 4G and L), obviously the result of a regular sequence of cell division (Text-figs. 4G, H, K) which had consisted of two vertical walls at