DR PETTIGREW ON THE PHYSIOLOGY OF WINGS. 401 



the insect, and this is accounted for by the circumstance, that in them the 

 muscles do not act exclusively at the root of the wing. In the bird and bat 

 the muscles run along the wing towards the tip for the purpose of flexing or 

 folding the wing prior to the up stroke, and for opening out or expanding it 

 prior to the down stroke. 



As the wing must be folded or flexed and opened out or expanded every 

 time the wing rises and falls, and as the muscles producing flexion and extension 

 are long muscles with long tendons, which act at long distances as long levers, 

 and comparatively slowly, it follows that the great short muscles (pectorals, &c.) 

 situated at the root of the wing must act slowly likewise, as the muscles of the 

 thorax and wing of necessity act together to produce one pulsation or vibration 

 of the wing. What the wing of the bat and bird loses in speed it gains in 

 power, the muscles of the bird and bat's wing acting directly upon the points 

 to be moved, and under the most favourable conditions. In the insect, on the 

 contrary, the muscles act indirectly, and consequently at a disadvantage. If the 

 pectorals only acted, they would act as short levers, and confer on the wing of 

 the bat and bird the rapidity peculiar to the wing of the insect. The tones 

 produced by the bird's wing would in this case be heightened. The swan in 

 flying produces a loud whistling sound, and the pheasant, partridge, and grouse 

 a sharp whirring noise like the stone of a knife-grinder. 



It is a mistake to suppose, as many do, that the tone or note produced by 

 the wing during its vibrations is a true indication of the number of beats made 

 by it in any given time. This will be at once understood, when I state that a 

 long wing will produce a higher note than a shorter one driven at the same 

 speed and having the same superficial area, from the fact that the tip and body 

 of the long wing will move through a greater space in a given time than the 

 tip and body of the shorter wing. This is occasioned by all wings being jointed 

 at their roots, the sweep made by the different parts of the wing in a given time 

 being longer or shorter in proportion to the length of the pinion. It ought, 

 moreover, not to be overlooked that in insects the notes produced are not 

 always referrible to the action of the wings, these, in many cases, being trace- 

 able to movements induced in the legs and other parts of the body. 



It is a curious circumstance that if portions be removed from the posterior 

 margins of the wings of a buzzing insect, such as the wasp, bee, blue-bottle fly, 

 &c, the note produced by the vibration of the pinions is raised in pitch. This 

 is explained by the fact that an insect, whose wings are curtailed, requires to 

 drive them at a much higher speed in order to sustain itself in the air. That 

 the velocity at which the wing is urged is instrumental in causing the sound, is 

 proved by the fact that in slow flying insects and birds no note is produced ; 

 whereas in those which urge the wing at a high speed, a note is elicited which 

 corresponds within certain limits to the number of vibrations and the form of 



