Lunar periodicity in reproduction

Abstract

In Volume 2 of the ‘ Philosophical Transactions ’ of the Royal Society, published in 1667, travellers to the East Indies are asked to enquire (p. 419) “ whether those shell-fishes, that are in these parts plump and in season at the full moon, and lean and out of season at the new, are found to have contrary constitutions in the East Indies ? ” This belief that the size of certain marine invertebrates, chiefly molluscs and echinoderms, varies with the phases of the moon is found in the literature of classical Greece and Rome and of the middle ages, and is held to-day in the fish markets around the Mediterranean and in the Red Sea. At Suez sea-urchins and crabs are said to be “ full ” at full moon and “ empty ” at new moon, at Alexandria the same thing is said of mussels and of sea-urchins, the Tarentines believe that oysters are fattest at full moon (34), while at Nice, Naples, Alexandria, and in Greece (17, p. 17, footnote) urchins are said to be fullest at full moon. The part of the sea-urchin which is eaten is the gonad, while in the crab it is the muscles, so that these tissues are supposed to vary in bulk with the phases of the moon. Now my own investigations, of which preliminary reports have already been published (8, 9) and a full account is to be given in this paper, have shown that while the supposition is untrue of mussels ( Mytilus sp .) and sea-urchins ( Strongylocentrotus lividus ) in the Mediterranean and of mussels ( Mytilus variabilis ) and crabs ( Neptunus pelagicus ) in the Red Sea, it is based on fact as concerns the sea-urchins found at Suez ( Centrechinus [ Diadema ] setosus ). In the last-mentioned form the gonads undergo a cycle of growth and development corresponding with each lunation throughout the breeding season. Just before full moon ovaries and testes are at their greatest bulk, filled with spermatozoa or eggs which are spawned into the sea at the time of full moon. The shrunken gonads then gradually fill again with ripening sexual products to be shed at the next full moon. It is remarkable, then, that a belief which was such common knowledge among the ancient inhabitants of Mediterranean countries that it was referred to by their poets and orators and one which is held to-day in the Mediterranean ports is indeed untrue of this region, while at Suez it is based on fact. It is possible that the Greeks originally obtained the belief from the ancient Egyptians, who would have it from the Red Sea (what really occurs there in sea-urchins being supposed to apply to all “ shell-fish ”), and that the same belief has survived around the Mediterranean until to-day. Or perhaps the belief had an independent origin in Greece, founded, not on fact, but on the supposed influence of the moon-deities on growth in general.