The oviducal gland of Octopus vulgaris is involved in the storage of spermatozoa and the production of an egg-laying cement. Spermatozoa are attached to the wall of spermathecae by means of their acrosome and retained there for several months before the maturity of the female. The cement (a mucoprotein) is synthesized in the peripheral part of the gland. In the central part a mucopolysaccharide is produced that acts as a polymerizer of the cement. This reaction was studied in vitro and some physical and chemical properties of the compounds are described. The cement serves finally to form an egg string for fixation to an appropriate substrate.