180 THE ZOOLOGIST. 



All the different kinds (of the large Dragonflies) when travelling 

 associate together, and occasionally, in a flight composed of 

 countless thousands, one of these brilliant-hued individuals will 

 catch the eye, appearing as conspicuous among the others as a 

 poppy or scarlet geranium growing alone in an otherwise flower- 

 less field. But the really wonderful thing about them all alike is, 

 that they appear only when flying before the south-west wind, 

 called pampero — the wind that blows from the interior of the 

 Pampas. The pampero is a dry, cold wind, exceedingly violent. 

 It bursts on the plains very suddenly, and usually lasts only a 

 short time, sometimes not more than ten minutes ; it comes 

 irregularly, and at all seasons of the year, but is most frequent in 

 the hot season, and after exceptionally sultry weather. It is in 

 summer and autumn that the large Dragonflies appear ; not with 

 the wind, but — and this is the most curious part of the matter — 

 in advance of it; and inasmuch as these insects are not seen in 

 the country at other times, and frequently appear in seasons of 

 prolonged drought, when all the marshes and water-courses for 

 many hundreds of miles are dry, they must, of course, traverse 

 immense distances, flying before the wind at a speed of seventy 

 or eighty miles an hour. On some occasions they appear almost 

 simultaneously with the wind, going by like a flash, and instantly 

 disappearing from sight. You have scarcely time to see them 

 before the wind strikes you. As a rule, however, they make their 

 appearance from five to fifteen minutes before the wind strikes ; 

 and when they are in great numbers the air, to a height of ten or 

 twelve feet above the surface of the ground, is all at once seen to 

 be full of them, rushing past with extraordinary velocity in a 

 north-easterly direction. In very oppressive weather, and when 

 the swiftly advancing pampero brings no moving mountains of 

 mingled cloud and dust, and is consequently not expected, the 

 sudden apparition of the Dragonfly is a most welcome one, for 

 then an immediate burst of cold wind is confidently looked for. 



It is clear that these great and frequent Dragonfly movements 

 are not explicable on any current hypothesis regarding the annual 

 migration of birds, the occasional migrations of butterflies, or the 

 migrations of some mammals, like the Reindeer and Buffalo of 

 Arctic America, which, according to Bae and other observers, 

 perform long journeys north and south at regular seasons, " from 

 a sense of polarity." Neither ibis hypothetical sense in animals, 



