Mechanism of the Spermatophoric Reaction in the Giant Octopus of the North Pacific, Octopus Dofleini Martini

In the giant octopus of the North Pacific, Octopus dofleini martini, the male reproductive tract contains up to 10 spermatophores. Each is about a metre long. It has a tube-shaped body surrounded by a tough, thin membrane, the 'outer tunic'. The body consists of two parts. The thicker part, which during copulation emerges first from the 'penis', contains the sperm rope with IO-IO tightly packed spermatozoa, surrounded by a viscous, colourless fluid, the spermatophoric plasma. The thinner part, which emerges second, consists of the rod-shaped, hyaline ejaculatory apparatus. The space between the sperm rope and ejaculatory apparatus is filled with the socalled cement liquid, usually amber coloured and even more viscous than the spermatophoric plasma. Attached to the thin distal end of the body is the 0-5 m long filamentous cap thread; this is the portion of the spermatophore, which is the last to emerge during copulation from the 'penis'. Copulation lasts about 2 h, during which time one or two spermatophores undergo the so-called spermatophoric reaction. As a result of this reaction the ejeculatory apparatus everts and the sperm rope advances the entire length of the spermatophore, to be finally ejected into the 'spermatophoric bladder', a portion of the tunic which assumes the size and shape of a hen's egg. Subsequently, the 'bladder' bursts inside the female's reproductive tract, releasing the spermatozoa. Fertilization then takes place, and the fertilized eggs are deposited in the sea water where further embryonic development follows. Some of the outstanding morphological and chemical characteristics of spermatozoa, and the main phases of the spermatophoric reaction in Octopus dofleini martini, have been described in the earlier papers (Mann, Martin & Thiersch, 1966, 1970; Martin, Thiersch, Dott, Harrison & Mann, 1970; Brooks, Lutwak-Mann, Mann & Martin, 1971; Mann, Karagiannidis & Martin, 1973; Martin, Lutwak-Mann, Mclntosh & Mann, 1973). Under in vitro conditions, that is, in a spermatophore extracted manually from the male's reproductive tract and transferred for observation into sea water, the start of the spermatophoric reaction is indicated by swelling of the spermatophore due to influx of sea water. The sperm rope begins to advance and uncoil, while the ejaculatory