154 FRANK R. LILLIE AND E. E. JUST. 



I. The Sivarms. — The swarms consist only of fully mature 

 males and females; indeed we never secured even a single swarm- 

 ing animal which was not fully mature, or which contained any 

 immature sexual elements mingled with the mature ones. The 

 occurrence of swarming is dependent more upon the lunar cycle 

 than any other factor; the relations with reference thereto are 

 given under the second heading, " The Runs.'" The second most 

 important factor in swarming is time of day; swarming begins 

 invariably soon after twilight and continues for an hour or two 

 at the most. A third factor is weather; very bad weather with 

 heavy wind and rain may prevent swarming, or at least prevent 

 the animals from coming near enough to the surface to be seen. 

 A fourth factor is light, partially included, of course, under the 

 second factor. But we have reference here especially to condi- 

 tions that occur at the time of full moon or a little later, when 

 swarming may begin after twilight, and be suddenly cut short 

 by the appearance of the moon above the eastern hills. ^ On the 

 other hand during the light of the moon, i. e., from shortly after 

 new moon until near the time of the full moon the animals do not 

 swarm even if the moon is entirely concealed by thick clouds.^ 

 The stage of the tide whether high or low was not an observable 

 factor at our station, where the range of tidal movement is only 

 about 1 8 inches. Neither do the summer variations in tempera- 

 ture appear to be an important factor; in any event the tempera- 

 ture of the water varies but little during the swarming season. 



We have gained the impression that all the absolutely mature 

 animals of any given locality swarm as soon as the right condi- 

 tions are offered. This would involve the assumption that the 

 maturing of the animals is dependent on some relation of the 

 life history to the phases of the moon, involving probably, 



1 An exception to this was noted at the time of full moon in July, 1912, when 

 after moonrise both males and females were abundant. (See curve i, July 28 and 29.) 



2 As an exception it may be noted that the end of the June run (191 2) extended 

 to within three days of the full moon (see curve 6). But the general rule is as 

 stated. Special attention was directed to this point both in 191 1 and 1 912. There 

 were several cloudy nights during the light of the moon in these years about the 

 time of the first quarter of the moon; for instance, on July 21, 1912, a hard rain 

 fell in the afternoon and the evening was dark and cloudy, but no worms could be 

 found. We often tried collecting in dark places under wharves, etc., on moonlit 

 nights, but always without success. 



