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L:M.B.C. MEMOTRS 
No. IV. CODIUM. 
BY 
R. J. Harvey Grsson, M.A., F.L.S., and Heten P. Avbp, B.Sc. 
INTRODUCTION. 
AmonG the heterogeneous collection of Alge, marine and 
fresh-water, known to Botanists as Chlorophyceex, none, 
perhaps, are more interesting from the morphological 
point of view than the Siphonexe. The interest attach- 
ing to them centres in the fact that the vegetative thallus, 
though not infrequently of immense size and complicated 
structure, is, in reality, produced by the extension, 
branching and modification of a single ‘‘cell” or cceno- 
cyte, possessed of an indefinite number of nuclei. In 
such forms as Valonia, the primitive spherical cell form 
is retained ; in Vaucheria, the thallus becomes filamentous 
and sparingly branched; in Caulerpa, Bryopsis, &c., the 
branching is more extensive and symmetrical. In other 
types, again, the thallus consists of an aggregation of 
hyphe, held together by a deposition of calcium carbonate, 
e.g., Halimeda, &c., by holdfasts of diverse form, ¢.g., 
Udotea, Struvea, &c., or by intimate interweaving of the 
filaments themselves, a mode of union illustrated by the 
subject of the present Memoir, viz., Codiwm, 
