352 DR PETTIGREW ON THE PHYSIOLOGY OF WINGS. 



iii a curve, which, of course, is equivalent to placing the wing above, and, so 

 to speak, behind the insect — in other words, to elevating the wing prepara- 

 tory to a second down stroke, as seen at g of figures 16 and 17, page 349/" 

 The Body ascends when the Wing descends, and vice versa. — The manner in 



which the body falls downwards and forwards in 

 progressive flight is illustrated at figs. 20, 21, and 

 22. 



At fig. 20 the body is represented at a and c, 

 the wing at b and d, x supplying the fulcrum or 

 • pivot on which the body and wing oscillate. 

 I If the body (a) is elevated in the direction 



e, the wing (b) of necessity descends in the direc- 

 tion h. If, on the other hand, the body (c) 

 descends in the direction /, the wing (d) ascends 

 -,//■ in the direction g. The ascent or descent of 



Fig. so. the wing is always very much greater than that 



of the body, from the fact of the pinion acting as 

 a long lever. The remarks just made are true more especially of the body 



* When a bird rises from the ground it runs for a short distance, or throws its body into the air 

 by a sudden leap, the wings being simultaneously elevated. When the body is fairly off the ground, 

 the wings, are made to descend with great vigour, and by their action to continue the upward impulse 

 secured by the preliminary run or leap. The body then falls in a curve downwards and forwards, the 

 wings, partly by the fall of the body, partly by the reaction of the air, on their under surface, and 

 partly by the contraction of the elevator muscles and elastic ligaments being placed above, and to 

 some extent behind the bird — in other words, elevated. The second down stroke is now given, and 

 the wings again elevated as explained, and so on " ad infinitum," the body falling when the wings are 

 being elevated, and vice versa, as shown at fig. 14, p. 344. When a long-winged oceanic bird rises 

 from the sea, it uses the tips of its wings as levers for forcing the body up, the points of the pinions 

 suffering no injury from being brought violently in contact with the water. A bird cannot be said to 

 be flying until the trunk is swinging forward in space and taking part in the movement. The hawk, 

 when fixed in the air over its quarry, is simply supporting itself. To fly, in the proper acceptation of 

 the term, implies to support and propel. This constitutes the difference between a bird and a balloon. 

 The bird can elevate and carry itself forward, the balloon can simply elevate itself, and must rise and 

 fall in a straight line in the absence of currents. When the gannet throws itself from a cliff the inertia 

 of the trunk at once comes into play, and relieves the bird from those herculean exertions required to 

 raise it from the water when it is once fairly settled thereon. A swallow dropping from the eaves of 

 a house, or a bat from a tower, afford illustrations of the same principle. Many insects launch them- 

 selves into space prior to flight. Some, however, do not. Thus the blow-fly can rise from a level sur- 

 face when its legs are removed. This is accounted for by the greater amplitude and more horizontal 

 play of the insect's wing as compared with that of the bat and bird, and likewise by the remarkable 

 reciprocating power which it possesses when the body of the insect is not moving forwards. ( Vide 

 figs. 3, 4, 5, and 6, page 338). When a beetle attempts to fly from the hand it extends its front 

 legs and flexes the back ones, and tdts its head and thorax upwards so as exactly to resemble a 

 horse in the act of rising from the ground. This preliminary over, whirr go its wings with immense 

 velocity, and in an almost horizontal direction, the body being inclined more or less vertically. The 

 insect rises very slowly, and often requires to make several attempts before it succeeds in launching 

 itself into the air. I could never detect any pressure communicated to the hand when the insect was 

 leaving it, from which I infer that it does not leap into the air. The bees, I am disposed to believe, 

 also rise without anything in the form of a leap or spring. I have often watched them leaving the 

 petals of flowers, and they always appeared to me to elevate themselves by the steady play of their 



