Lunar Periodicily 219 



though these are generally less extensive. Many animals move from 

 the surface to deeper levels in the soil at regular periods each day. 

 Others emerge from under the ground litter at definite times during 

 the diurnal cycle and ascend the vegetation. Harvestmen, or "daddy- 

 long-legs" {Leiobunlum rotunduin), in an English oak wood were 

 observed to descend from the tree trunks in the evening to the forest 

 floor where they hunt their prey and to move up onto the trees again 

 in the early morning (Todd, 1949). Many other insects move reg- 

 ularly from lower levels in the herbs and shrubs to higher positions 

 in the trees at dawn and return at dusk; others migrate in the reverse 

 manner. These changes in levels of whole populations, both in the 

 water and on land, have profound repercussions on prey-predator 

 relations and other interdependencies among the inhabitants. For 

 a further discussion of these aspects of stratification and periodicity 

 in the community, the reader should refer to Alice et al. ( 1949, Ch. 

 28). 



Lunar Periodicity. Since the days of classical Greece interest has 

 been attracted to the correlation of certain animal activities with pe- 

 riods of the moon. Oppian in the time of Aristotle wrote: 



The shellfish which creep in the sea are reported, all of them when the 

 moon waxes, to fill up their flesh proportionately to her disk, occupying then 

 a bigger space, On the other hand when she wanes they shrivel and their 

 members grow thinner. 



It is true that in the Red Sea the gonads of the sea urchins ( the edible 

 portion) do enlarge during the period of the full moon, but the be- 

 lief was spread fallaciously around the Mediterranean and elsewhere 

 that the lunar cycle controlled many more animal activities than is 

 actually the case. One even meets the statement occasionally that 

 the 28-day menstrual period in man harks back to our marine an- 

 cestors. Since we know that the menstrual cycle in other mammals 

 has very different periods, the agreement of the human period with 

 the 28-day lunar cycle is merely a coincidence. 



Modern investigation has shown that the activity of certain widely 

 different types of organisms, usually in relation to the reproductive 

 cycle, shows a correlation with the moon. The striking nature of 

 these lunar periodicities is well illustrated by the fluctuation in the 

 abundance of conjugants produced by a ciliate living as an ectopara- 

 site on the gills of a fresh-water mussel (Fig. 6.18). The distinct 

 peaks occurred regularly on the days following the new moon and 

 were not correlated with temperature or other known environmental 

 changes. 



