SOUNDS PRODUCED BY INSECTS. 217 



undetermined whether the sounds produced by the inferior larynx, are the 

 result of the vibrations of a reed- or tongue-like apparatus, or whether they 

 are caused by the friction of a column of air against the margins of an opening. 

 In those birds provided with a simple vocal apparatus, such as the duck, there 

 can be no doubt that this is reed-like in character ; for when in action, the 

 margins of the membranes can be seen to vibrate, an'd the resulting sound is, 

 besides, exactly analogous to that produced by elastic membranes when thrown 

 into vibrations. An opinion has been entertained by some, that the varied and 

 manifold tones, which singing birds, provided with a more highly-developed 

 inferior larynx, are able to produce, are due to sonorous vibrations in a column 

 of air, excited by friction against the margins of the aperture of the inferior 

 larynx, in the same manner as the sound in whistling is produced by the fric- 

 tion of the air against the margins of the lips ; but even admitting this to be 

 true, the vibrations of the air must, in their turn, communicate vibrations to 

 the vocal membranes. The range of the voice in Birds is usually within an 

 octave, but in some it is much greater. As in Mammalia, the voice is always 

 in a minor key. The various notes are produced, not only by changes in the 

 degree of tension of the vocal membranes, but by differences in the force of the 

 blast of air, and by changes in the length and degree of tension of the trachea, 

 or of other resounding parts. 



The trachea presents various modifications in different birds. In some, it is 

 much longer than the neck, forming a folded tube, which consists of a vast 

 number of rings, as in the capercailzie, stork, crane, and wild swan ; in the 

 flamingo, these rings are said to be about 350 in number. In some birds, the 

 trachea is wider above than below, and in others, it is dilated at various points. 



In Keptiles, the vocal organs are of a more simple character than in Mam- 

 malia and Birds, though they present many different degrees of development 

 in the various Orders and Genera. The vocal cords are absent in the true 

 Serpents, which therefore possess no voice, properly so-called ; the hissing 

 sounds produced by them, result from a forcible breathing through a soft glot- 

 tis. In frogs, amongst the Amphibia, the larynx opens directly into the 

 bronchi, these animals being unprovided with a trachea ; the intensity of the 

 sounds emitted by the male frog,' is much increased by the presence of mem- 

 branous sacs at the sides of the neck, which undergo considerable distension 

 during croaking. Some frogs possess membranous vocal cords. In others, 

 the organs which emit sound, consist of two solid rod-like bodies, the anterior 

 ends of Which are fixed, whilst the posterior extremities are free, and are di- 

 rected towards the orifice of the bronchus on either side. 



Fish, when taken out of water, make a peculiar noise ; this is caused by the 

 sucking or flapping movements of their mouths or gill-coverings. A few fish, 

 provided with an air-bladder opening into the pharynx, probably produce 

 sounds by the compression of this organ. The tambour fish produces contin- 

 uous sounds when under water ; its air-bladder is of large size, and is exceed- 

 ingly muscular. 



A certain number of Insects can produce sounds. In some, as for example, 

 the Coleoptera or beetle tribe, the blue-bottle flies, and humble-bees, the sounds 

 are said to result from the passage of air through their spiracles, constituting 

 what is termed humming or purring. In others, such as the crickets and 

 grasshoppers, the sounds are caused by the friction of file-like organs, upon 

 the margin of membranous drums, which are formed upon the wings, and the 

 sound is called stridulation. The pitch of the sound of the cricket is very high, 

 being produced by 4096 vibrations in a second. The noises in certain species 

 are dependent on the rapid movements of folded membranes, called the tim- 

 bales, which are inclosed, one on each side, in a -cavity on the under part of 

 the abdomen, and which are moved by the contraction and relaxation of spe- 

 cial bands of parallel muscular fibres. It was long since shown that in the 

 Dipterous Insects, such as the flies and gnats, which have only two wings, the 

 buzzing sound is totally independent of the action of the wings in flight, for 

 these may be cut oft; and yet the sounds are still heard ; they are produced by 

 the rapid vibration of two lateral appendages named lialteres, which are rudi- 

 mentary posterior wings. The noise emitted by the sphinx, or death's-head 



