244 ON INSECT SOUNDS. 



this part in which the trachea? are so minutely distributed, exert 

 great influence upon the sounds produced. The vocal bands do 

 not always require to be set singing by air expired throuo-h the 

 apparatus j for the tone depends upon the quantity of air, and the 

 rapidity of its motion, and upon the tension of the elastic ring in 

 which the vocal bands are stretched. 



The other insect sounds are more simply produced. The wing 

 tone of many insects, flies, bees, and beetles — is due to rapid 

 vibration of wings. In other cases as in crickets, grasshoppers, 

 locusts and some water beetles, the wing covers are set in vibration 

 by friction of notched ribs on the wing covers. In others again 

 different parts of the body are provided with rasp edges and borders, 

 as with the goat beetles, dung beetles, burying beetles, also the 

 bees, ants, kc. Occasionally special resounding apparatus is met 

 with, as in the case of the arched thoracic ring of the goat beetle, 

 which vibrates powerfully with the underlying tracheae, and in 

 other cases the wing covers (of the cricket for instance) the 

 abdomen or even the whole external chitinous skin, as may be 

 felt when holding a fly between the fingers. 



6. Muscle action in production of sounds. 



In all rasping sounds the movement of limbs necessary to set 

 wing cases in vibration, must be considered voluntary. In the 

 special vocal stigmata of insects so provided, muscles and nerves 

 may be found. In the flies the vocal ring and the edges of the 

 valves are acted upon by muscles. The vocal ring is capable of a 

 double movement, it can be drawn out in the vertical direction by 

 muscle effort and retracted again by the elastic power of the ring 

 itself. The effect of this movement is that the vocal ring which 

 carries the vocal membrane may be lengthened and the edges of 

 the vocal membranes thereby approximated, narrowing the chink 

 between them, whilst at the same time they are tightened. Prof. 

 Landois observed this action in an insect dissected and placed 

 under the microscope. The sound issued whenever the muscle 

 acted, and ceased when the vocal ring and its rings were relaxed. 



