146 RHYTHM 



certain marine worms in Japan and in the Atlantic, which 

 show a similar rhythm. 



A somewhat similar state of things has been observed in 

 a marine worm known as Odontosyllis enopla which occurs in 

 the Bermudas. It reproduces three times a year, at the first 

 low tide in July, the moon being in its last quarter; then again 

 26 days later and in less abundance; and after an interval 

 of 26 or 27 days, i.e. late in August. They appear on the 

 surface at dusk, usually within five minutes of eight, and 

 the phosphorescent display is always over by half-past eight. 

 At first the female, swimming on the surface of the sea, shows 

 no light, but quite suddenly she becomes markedly phos- 

 phorescent, swimming through the water in small luminous 

 circles. Around this circle is a halo of phosphorescence. If 

 the male does not appear the illumination ceases after ten 

 or twenty seconds, though it may be repeated four or five 

 times. Usually, however, the males are abundant, and unmated 

 females are rare. The male appears as a glint of light at first 

 some ten or fifteen feet from the luminous female. It comes 

 up obliquely from the deeper waters and darts at the centre 

 of the luminous circles, finding the female with remarkable 

 precision. The two then rotate, performing a kind of cere- 

 monial dance, scattering and shedding eggs and sperm in the 

 water. 



Then again, that curious mollusc with its segmented shell, 

 the Chiton, breeds only at the time of full moon in certain 

 parts of the world. It has even been said that the number 

 of births in large human communities show a certain corre- 

 lation with the sidereal lunar period of 27-3 days. This is 

 the time taken by the moon in making one circuit of the 

 heavens. 



It has been pointed out that during the last century and a 

 half the maximum and minimum herring fisheries have coin- 

 cided with the maximum and minimum declination of the 

 moon, which occurs at intervals of just over nine years. Both 

 in Denmark, in Italy and in Egj^pt the eel fishermen maintain 

 that their best catches are always taken when there is no 

 moon; and it is on record that strong lights will check or 

 retard the migration of these fishes up the rivers. 



