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