Many animals have powers by which they are able to act in concert at times, vast numbers of them moving in unison over immense areas by signals or intuitions which man can neither imitate nor understand. Such are the mysterious migrations of the Norway lemming and of many birds and insects, and such were the memorable stampedes of the bison hordes on the American plains in years gone by. Kropotkin saw on the Siberian steppes one autumn ‘thousands and thousands’ of fallow deer come together from an area as large as Great Britain at a point on the Amur River in an unprecedented exodus to the lowlands on the other side.[2] How these scattered thousands knew when to start so as to arrive at the river at the same time, and how they knew the direction to travel and found their way so well, are mysteries which man can as yet only wonder at. More marvellous yet—more marvellous, perhaps, than the concurrent action of any other animal, for it implies the most accurate time-keeping extending over many years—are the annual festivals of the _palolo_, an annelid living among the interstices of the coral reefs of some of the islands of the South Pacific. About three o’clock on the morning following the third quarter of the October moon, these worms invariably appear on the surface of the sea, swarming in great numbers. Just after sunrise their bodies begin to break to pieces, and by nine o’clock no trace of them is left. On the morning following the third quarter of the November moon they appear again, but usually in smaller numbers. After that they are seen no more till the next October. This annual swarming is a phenomenon connected with reproduction, the ova escaping from the broken bodies of the females and, after being fertilised by the free-floating sperms, sinking down among the coral reefs and hatching into a new generation. ‘Year after year these creatures appear according to lunar time. And yet in the long-run they keep solar time. They keep two cycles, one of three and one of twenty-nine years. In the three-year cycle there are two intervals of twelve lunations and one of thirteen lunations. These thirty-seven lunations bring lunar time somewhat near to solar time. But in twenty-nine years there is enough difference to require the addition of another lunation; the twenty-ninth year is therefore one of thirteen instead of twelve lunations. In this way they do not change their season in an entire century. So unfailing is their appearance that in Samoa they have given their name to the spring season, which is called “the time of the palolo.”’