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Show 802 DR. J. MURIE ON THE ANATOMY OF OTARIA JUBATA. [Dec. 6, thus happens here with the large Owl, the Adjutant, and other species that fly singly or in small flocks: a few first appear like harbingers ; these are soon joined by new comers in considerable numbers ; and before long they are in myriads. Inconceivable numbers of birds are, no doubt, continually passing over us unseen. It was once a matter of wonder to me that flocks of Swans should almost always appear flying past after a shower, even when none had been visible for a long time before, and when they must have come from great distances. But the simple reason soon occurred to me, that after rain a Swan may be visible at a vastly greater distance than during fair weather, the sun shining on its snow-white plumage against the dark background of a cloud rendering it very conspicuous. The fact of Swans being seen almost always after a rain is only a proof that they are almost always passing. Whenever we are visited by a great dust-storm, myriads of Gulls appear flying before it; this is invariably the case even when not a Gull has been visible for months. A dust-storm is always preceded by long drought, so that from the watercourses being all dry the Gulls could not well have subsisted in the region over which it passes. Yet in seasons of drought Gulls must be incessantly passing over us, visible only when driven together and forced towards the earth by the violence of the storm. The bird I allude to is the Black-headed Gull (Larus cirrhocephalus). In seasons when Grasshoppers abound very much, flocks of these birds also appear, often in such multitudes as to free entire districts from the devastating swarms of the hated insects. It is a fine sight, and a welcome one as well, to see a flight of these birds settle on the afflicted district; at such times their mode of proceeding is often so regular, that a body of them well deserves the appellation of ' an army of birds.' They come down with a swift graceful flight, and settle on the earth with loud joyful cries, but do not abandon when the work of devouring has begun the order in which the flock was disposed. It often presents a front of several thousand feet, with a breadth of but sixty or eighty; all along this line of battle the excited cries of the innumerable birds produce a loud, incessant noise. Every bird is incessantly on the move-some skimming along the ground with half expanded wing, others pursuing the fugitives through the air; and all the time the hindmost birds are flying over the flock and alighting in the front ranks ; so that the whole body is steadily advancing, and leaving the earth over which it passes free from the pest. The Black-headed Gull is one of our most common birds, and has many very interesting habits ; I hope before long to make it the subject of another letter. " I remain, Sir, " Truly vours, " W. H. HUDSON." Dr. J. Murie read the second part of his memoir on the AAnatomy of the Sea-lion (Otaria jubata). The present portion treated of the skeleton and nervous system, vascular and respiratory organs, di- |