In the spring of 1900 a great migration of dragon-flies was observed in Belgium. “All the observers agree that the insects flew rather low, with astonishing regularity, and without resting; that they kept close to the earth, where there were no obstacles, but that they mounted to a height of 10 to 12 mètres when houses or trees were in the way. They did not go round obstacles in their line of route, but surmounted them, and descended on the other side. According to some observers, their flight was very slow, others again asserting that it was very swift. When the velocity could be estimated, however, it was found to be at 5 mètres per second or 18 kilometres (11¼ miles) per hour (so that the slows have it). In general they went in groups, more or less isolated, and more or less dense.” The writer of the above account—a Belgian—concludes thus: “All the facts point to the following conclusions: The dragon-flies of the 5th came from regions situated to the east of the country, which they entered in several columns, flying at a great altitude: between 7 and 8 a.m. they descended towards the earth, continuing their route towards the west. But we remain in ignorance of their point of departure. The swarm probably quitted its usual habitation early in the morning, and immediately flew to a great height. It was only on arriving near the earth that they flew against the wind”[41] (which, however, they then continued to do). What Mr. Hudson calls “dragon-fly storms” are a special phenomenon of the Pampas. In this case the cause of the migration—for such movements seem to come under this heading—is a special wind called the _pampero_, that blows south-west from the interior of the Pampas. It is very violent, cold, and dry, and the dragon-flies evidently fear it. The “storm” is thus described by Mr. Hudson: “It is in summer and autumn that the large dragon-flies 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 watercourses for many hundreds of miles are dry, they must, of course, traverse immense distances, flying before the wind at a speed of 70 or 80 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 5 to 15 minutes before the wind strikes; and when they are in great numbers, the air, to a height of 10 or 12 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