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 dragon-fly is a most welcome one, for then an immediate burst of cold wind is confidently looked for. In the expressive vernacular of the gauchos the large dragon-fly is called _hijo del pampero_--son of the south-west wind. It is clear that these great and frequent dragonfly movements are not explicable on any current hypothesis regarding the annual migrations of birds, the occasional migrations of butterflies, or the migrations of some mammals, like the reindeer and buffalo of Arctic America, which, according to Rae and other observers, perform long journeys north and south at regular seasons, "from a sense of polarity." Neither this hypothetical sense in animals, nor "historical memory" will account for the dragon-fly storms, as the phenomenon of the pampas might be called, since the insects do not pass and repass between "breeding and subsistence areas," but all journey in a north-easterly direction; and of the countless millions flying like thistledown before the great pampero wind, not one solitary traveller ever returns. The cause of the flight is probably dynamical, affecting the insects with a sudden panic, and compelling them to rush away before the approaching tempest. The mystery is that they should fly from the wind before it reaches them, and yet travel in the same direction with it. When they pass over the level, treeless country, not one insect lags behind, or permits the wind to overtake it; but, on arriving at a wood or large plantation they swarm into it, as if seeking shelter from some swift-pursuing enemy, and on such occasions they sometimes remain clinging to the trees while the wind spends its force. This is particularly the case when the wind blows up at a late hour of the day; then, on the following morning, the dragon-flies are seen clustering to the foliage in such numbers that many trees are covered with them, a large tree often appearing as if hung with curtains of some brown glistening material, too thick to show the green leaves beneath.