LUNAR PERIODICITY IN LIVING ORGANISMS 277 



is no lunar reproductive cycle. The Alexandrian species is 

 identical with one of those fished and eaten at Naples, which, 

 as mentioned above, has apparently no lunar cycle. How, then, 

 are we to account for the ancient Greek and Roman belief in 

 such a periodicity, and for the present-day statements in the 

 Naples and Alexandria fish markets ? I can only suppose that 

 what is a fact at Suez has come uncritically to be believed all 

 over Egypt, and that in very early times the Egyptian belief 

 was brought to Greece, whence it spread, and has remained all 

 around the Mediterranean coasts. 



In addition to sea-urchins, it is believed in the Egyptian 

 fish-markets that the flesh of mussels and crabs varies in quantity 

 with the moon. In mussels, just as in sea-urchins, the genital 

 glands form the bulk of the edible material, in crabs it is the 

 muscular tissue. It is these tissues, then, that are supposed to 

 vary in bulk with the changing moon, but I have found that 

 this is not true. Presumably what really occurs in the sea- 

 urchins is imagined by the people to take place in all " shell- 

 fish." 



The eggs of the sea-urchin when spawned into the sea are 

 normally fertilised immediately by spermatozoa shed by a 

 neighbouring male. In the course of a few hours the segmenting 

 eggs develop into free-swimming ciliated larvae which rise to 

 the surface of the sea, where they become members of the great 

 floating population known as the plankton. Now it is obvious 

 that the periodic spawning of Diadema must be reflected in the 

 plankton of the Gulf of Suez. The larvae of this sea-urchin 

 swimming at the surface of the sea must vary in numbers and 

 in stage of development with the phases of the moon. In the 

 same way there must be a lunar periodicity in the frequency of 

 the pelagic larvae of all other animals which have a lunar repro- 

 ductive cycle. By studying plankton from different parts of 

 the world I hope to discover which these animals are. 



Up to the present the best known case of lunar reproductive 

 periodicity scientifically investigated has been that of the 

 Palolo Worm (Friedlander, Biol. Centralbl., 1 898-1901). This 

 Polychaete {Eunice viridis) lives in the coral reefs in Samoa and 

 other Pacific Islands. At the last quarter of the moon in 

 October and November the posterior parts of the worms laden 

 with genital products become detached from the anterior 

 portions. While the latter remain among the coral the genital 

 segments swim up to the surface of the sea, where they shed 

 their spermatozoa and eggs. This swarming takes place at low 

 tide on several successive days, the swarms being composed 

 of enormous numbers of individuals which die after having 

 spawned. The swarming worms are fished by the natives who 

 relish them as a delicacy, and each year the fishermen judge 



