220 



Light 



Sept. Oct. Nov. Dec. Jan. Feb. 



Fig. 6.18. Average daily number of conjugants of the ciliate Conchophtliirius 

 la7nellidens on the gills of the fresh-water mussel Lamellidens niarginalis. Dates 

 of new moon ( top ) and of peak numbers are shown. ( Ray and Chakraverty, 



1934, Nature.) 



Most of the organisms exhibiting lunar periodicities are marine and 

 hence may be affected by the ampHtude of the tide which is greatest 

 at times of new moon and full moon (spring tides) and smallest at 

 the times of the quarter moon (neap tides). For organisms living 

 within the influence of the tides it is obviously difficult to determine 

 how much of the effect may be due to moonlight itself and how much 

 to the action of the tidal cycle. The marine alga, Dictyota, for ex- 

 ample, produces its gametes at the time of the full-moon spring tide. 

 The spawning of a number of marine polychaete worms shows various 

 time correlations. The palolo worm inhabiting the waters of the 

 South Pacific islands comes to the surface in great numbers on the 

 last quarter of the moon during October and November, producing a 

 luminescence and discharging eggs and sperm into the water. The 

 natives know of the occurrence of this swarming of the palolo worm 

 and take advantage of the opportunity to scoop up large quantities 

 of these animals for food. The worms swim about in small circles in 

 dense masses, giving the sea an appearance of spaghetti soup. The 

 natives gather the worms in crude baskets and celebrate the occasion 

 with religious rites and feasts. 



The Bermuda fireworm puts on a similar display of fireworks in the 

 shallow water early in the evening at the time of full moon. The 

 reaction appears to be set off by the drop in light intensity following 

 sunset (Huntsman, 1948). Professor E. L. Mark, who was for years 



