206 Papers from the Department of Marine Biology. 



Thus it appears that the migration of July 11, occurring simultane- 

 ously at Rebecca Shoal and Loggerhead Key, presented a front of at 

 least 20 miles. The individuals which actually alighted upon the 

 station were, of course, only a small percentage of those which crossed 

 the open sea within the visual radius of 13 miles; only those which came 

 very close could have been attracted by any slight odors emanating 

 from the lighthouse. Although Loggerhead Key is three-fourths of a 

 mile long and hence much larger than Rebecca Shoal station, it still 

 represents a small area on the surface of the sea. From these data one 

 hesitates to compute the possible numbers of mosquitoes that were 

 carried out to sea by the wind blowing from the Cuban coast. 



On July 18, 1 was transferred from Rebecca Shoal to the Tortugas, 

 where observations were continued. The wind held in the east for the 

 10 days of my stay there, so that no opportunity arose to witness 

 another mosquito migration. Attention was turned toward a deter- 

 mination of the numbers and species of the mosquitoes still present 

 on the islands, and their possible breeding-places. 



As stated by Dr. Mayer, the veering of the wind on the night of 

 July 11-12 caused a marked decrease in the numbers of mosquitoes 

 encountered in the vicinity of the laboratory; still it was possible 

 10 days later to attract considerable numbers of Aedes niger by 

 stationing one's self quietly in the shade near the bay cedar bushes. 

 On July 22 mosquitoes in one of the laboratories were so numerous that 

 4 were taken in one sweep of the net. Again on July 23, in the half 

 hour just preceding darkness, 11 specimens were caught. 



Since there are no swamps on the small sandy keys, the only breeding- 

 places for mosquitoes are such receptacles as may be maintained or 

 left by man. Examination showed that no larvee were present in the 

 fresh-water storage reservoirs at the laboratory or at the Loggerhead 

 light-station. It was thought likely that mosquitoes might be breeding 

 in cans thrown upon a waste pile among the bay cedar bushes. On 

 investigation many were found that contained rain-water but no larvse. 

 In short, not a single larva was found on Loggerhead Key during my 

 visit. Nevertheless, one small batch had, earlier in the season, ma- 

 tured in a shallow pool on a cement floor beneath the refrigerator, and 

 the possibihty is not excluded that Stegomyia calopus may have been 

 breeding there late in July; several specimens of this species were cap- 

 tured about the laboratory. But that Aedes niger or sollicitans were 

 breeding at that time is extremely doubtful, for both requii'e brackish 

 water for their development, and all the receptacles contained only 

 fresh water. Not only in the vicinity of the laboratory was it easy 

 to obtain specimens; they were distributed over the entire key. In 

 the early morning, afternoon, and evening A. niger could be attracted 

 from the grass and bay cedar bushes. 



The conditions on another of the Tortugas Islands are interesting 

 in this regard. East Key hes 6 miles east of Loggerhead and is the 



