208 Papers from the Department of Marine Biology. 



introduced by boats or had flown across the sea. That boats are 

 responsible for the presence of a few flies at the station was shown when 

 the small auxihary catboat brought one of the assistant keepers from 

 Key West ; 3 house-flies were found upon it as it was raised from the 

 water to the platform. Mr. Roberts, the assistant, stated that the 

 flies had annoyed him during the trip from the Marquesas Keys to 

 Rebecca Shoal that day. 



No more specimens were taken during the next 8 days, as will appear 

 from the table on page 202. It is important to note that not even 

 with the swarm of mosquitoes which arrived on July 5 were any house- 

 flies noted. But on July 6, following the sudden change of the wind 

 from north to east late on the preceding day, the hghthouse by con- 

 trast seemed fairly alive with Musca domestica; 25 were captured during 

 the day— 3 between 6 and 7^30°^ a. m. ; 1 each at 9^20^", 9^40"^, 10^55"^, 

 11^30'", 11^^32"; 10 between 11^33'" and I^IS""; 2 at 2^^10°' p. m.; 1 at 

 3 p. m.; 2 at 4*^20"; 1 at 5^15™, and the last at 5^25™. 



I am at a loss to account for the flight of house-flies from the east, 

 since no such numbers had come to the station on the east winds which 

 prevailed from June 26 to July 2. Had they arrived along with the 

 mosquitoes on July 5 the obvious assumption would have been that 

 they had come from the coast of Florida, but the fact that none 

 appeared until 12 hours after the wind had veered into the east seems 

 rather to point to Marquesas or some island farther east along the reef 

 as their source. That it would have been possible, as far as distance 

 is concerned, for the flies to have been carried from Key West 46 miles 

 to the east, will appear after a statement of the conditions under which 

 the second notable migration of Musca domestica appeared at Rebecca 

 Shoal, but the reason for their leaving an eastern point in such large 

 numbers at this time is still hidden; possibly the sudden change in the 

 direction of the wind took them unawares. 



During the 7th, 8th, and 9th of July the wind continued to blow 

 hghtly from the east. On the 7th of July, 5 flies were taken, 2 of them 

 at 5^30" a. m.; 1 at 6 and 2 at 12^30"" p. m. July 8 brought 5 more, 

 1 at 9M0"^ a. m. ; 2 at 12^30'"; 1 at 2i^30™, and 1 at 5^20™. A specimen 

 was captured at 5^10™ a. m. on July 9, another at 11^30™, and a third at 

 6 p. m. ; none appeared on July 10 while the wind was shifting toward 

 the south, but on the memorable 11th, along with 37 mosquitoes, came 

 18 house-flies from Cuba. It is interesting to note that, whereas the 

 mosquitoes were captured at all hours of the day as thej'' reached the 

 station, these flies were all taken between 9^50°" and 11^42™ a. m., 1 

 hour and 52 minutes. A possible explanation suggests itself. It will 

 be remembered that no Musca domestica accompanied the mosquitoes 

 from the coast of Florida on the north wind of July 4 and 5, but the very 

 shortest distance in that direction is 105 miles. Now, the distance 

 from Rebecca Shoal to the coast of Cuba is 10 miles less or about 95 



