_The Raven, corvus corax._—The raven of Europe differs in some respects from that of America. In Great Britain it is not an uncommon bird. It is said if a man in England, at any moment, throw himself on the ground, in the fields, more especially if he lie motionless on his back in the position of a lifeless body, a raven will be found to draw near, and reconnoitre, though unseen a moment before. This fact would seem to confirm the opinions doubted by Mr. Knapp—that sight, and not smell, is the sense by which these birds are guided in descending on their prey, since the mere motionless feigning of death is sufficient to attract their attention. It is well known that Mr. Audubon held this opinion, confirming it by experiments with the American turkey-buzzards, which proved quite inattentive to carrion of the most offensive kind when placed immediately before them, so long as it was concealed from their sight by a cloth. Dr. James Johnson and other writers on the subject also doubt the sense of smell in birds of this habit, and other experiments like that of Mr. Audubon have had the same result. Owing to the greater care bestowed on the health of cattle at the present day, and their less frequent deaths in the field under the modern system, ravens are said to be sensibly diminishing in England. NOTE V. THE HOUSE FLY, (_musca carnaria_,) p. 151. The speed of these familiar insects when on the wing, is very remarkable, being computed at a third of a mile in a minute. The peculiarity of their walking, apparently against the laws of gravitation, with such perfect ease, has been the subject of much investigation and controversy. Formerly it was believed that the fly walked by means of organs called suckers, which produced a vacuum at the extremity of each foot, by exhausting the air. Some lizards are known to climb walls in this way. But it is now more generally believed that the firm hold of the house fly is more simple, provided by fine, hairy appendages to the feet, by which they cling to the most minute inequalities of our walls and windows. Flies feed chiefly on liquids, and the juice of solid substances; they are also enabled to dissolve certain solids, by means of a saliva, which they eject for the purpose, on sugar, &c. The familiar sound produced by flies, comes from their wings; but as many winged insects move silently, the air must act upon those of the fly in a peculiar manner. NOTE W. THE ROBIN, page 164.