ii 4 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 large- 

 ly 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 Man- 

 chester, Liverpool, Birmingham, etc. They are, in fact, 'the poor 

 man's oyster.' So much, indeed, are mussels used as food, that a prop- 

 osition 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 retail- 

 ers 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." Zand and 

 Water. 







HOW INSECTS DIEECT THEIE FLIGHT.* 



By M. J. DE BELLESME. 



THE works of M. Marey have nicely determined the difference be- 

 tween 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 ev- 

 ery 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 

 {Vaxe de sustention). Both these elements are sometimes movable, but 

 more often it is the center of gravity which changes. 



* From a paper read before the Paris Academy of Sciences, and published in " Comptes 

 Rendus." Translated by M. Howland. 



