Page:Popular Science Monthly Volume 17.djvu/124

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114
THE POPULAR SCIENCE MONTHLY.

five-fingers, or star-fish, and whelk-tingles. It is most interesting to watch the five-fingers eating the mussels. The whelk-tingles, or white buckies, as they are called at Montrose, will clear off in a few hours a large acreage of mussels. The proprietors, therefore, employ women and children to pick them off at low tide. Not only are mussels largely used as bait, but they are a favorite food of the poor, and are sold in large quantities in the streets of the large towns of England—Manchester, Liverpool, Birmingham, etc. They are, in fact, 'the poor man's oyster.' So much, indeed, are mussels used as food, that a proposition was more than once seriously made to us by the fishermen that it should be illegal to use mussels for human food. As regards their value as food, I have made the following calculation: There are on the average thirty-nine mussels to the pound, equal to 87,360 mussels in a ton. These cost first hand £1 5s. per ton; the cost to the retailers is £3 6s. 8d. per ton. In March, 1876, a large number of crows were observed eating mussels (query, fresh-water) in the Norfolk Broads. There are large quantities of mussels in many of the broads and rivers, especially in South Walsham Broad, and also, I believe, in Hoveton Broad, Ormesby Broad, and Fritton Water. At the present time I believe no use whatever is made of them; it is as well to see if these mussels can not be cultivated and used for bait."—Land and Water.

 
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HOW INSECTS DIRECT THEIR FLIGHT.[1]
By M. J. DE BELLESME.

THE works of M. Marey have nicely determined the difference between the manner in which birds and insects fly. The bird can change at will the angle of vibration of his wings, and therefore these organs serve to steer his flight. The insect is deprived of this power, because the angle of vibration, as a rule, is invariable in each species, the flying-muscles not being in the wings, but in that part of the thorax which supports the wings.

Knowing these facts, I concluded that if the wing of the insect be merely a motor apparatus, the steering function must be sought for elsewhere; and, from numerous experiments made upon insects of every order, I am convinced that the steering power depends upon the position of the head and thorax, this, in its turn, depending upon the respective positions of the center of gravity and the axis of suspension {l’axe de sustention). Both these elements are sometimes movable, but more often it is the center of gravity which changes.

  1. From a paper read before the Paris Academy of Sciences, and published in "Comptes Rendus." Translated by M. Howland.