2^2 ON INSECT SOUNDS. 



brought by muscular action. Another circumstance which must 

 affect the change of note is the probable change of current of air 

 drawn into the body or forced out of it. It is well known that a 

 tongue of metal set in vibration by holding the frame in which it 

 is set;, close to the lips, gives a different note, when air is drawn 

 into the mouth, from that which is produced by blowing out- 

 wards. A difference of a half note is frequently observed. 



Difference of sex of insect affects the voice only in so far as the 

 voice apparatus is larger or smaller. Being for the most part 

 larger in the female insect, the male voice is mostly higher in 

 pitch ! 



5. The mechanism of vocal sounds. 



The instruments we employ to produce musical sounds, are 

 principally organ pipes (open and stopped as in diapason, flute, &c.) 

 reed pipes (clarinet, oboe, &:c.) bells, bars, strings, tuning forks, &c • 

 The insect voice apparatus may be compared with reed pipes in 

 their action, since a membrane is set in free vibration at the end, 

 or near to the open mouth of the breathing tube. This breathing 

 tube (trachea) represents a pipe which ramifies in a wonderful 

 series of branching twigs distributed throughout the interior of the 

 insect body. The terminal trunks of this tree open upon the 

 surface of the body by mouths (stigmata) which may be seen on 

 each side of the Thorax and Abdomen. The larger trunks 

 within the body are connected by transverse tubes and in many 

 insects larger expansions of the tracheae are found which constitute 

 a special apparatus enabling the insect to store a relatively large 

 volume of air which it can force by muscle pressure through the 

 vocal organ. Thus for instance in the '" blue bottle " fly there are 

 found two large tracheal sacs or bladders occupying a space in the 

 back of the body which act as bellows. Before the tracheal tube 

 reaches the locality of the vocal apparatus, it contracts somewhat 

 in dimension; a vocal apparatus is only observed in the thoracic 

 tracheal tubes. 



The reed or tongue (vocal apparatus) is represented by minute 



