INSECTS AND PLANTS 61 



for the true sound organs, but they are rather sounding 

 boards, or drums, to increase and transmit the sound vibra- 

 tions induced by the play of the timbals. That they are 

 not essential to the production of sound can be shown by 

 slitting them or removing them altogether without there 

 being any cessation of the note. Much more important 

 modifiers of sound are the semicircular discs projecting from 

 the thorax over the ' mirrors,' which, if closed artificially 

 or by the insect, deaden the sound very much, or, if opened 

 or cut off, allow it to escape in greater volume. In singing 

 also the insect modifies its song notes and their volume by 

 raising and lowering the abdomen, thus opening and closing 

 these discs ; and the act of singing is also accompanied by 

 a sort of trembling of the thorax. The position assumed 

 by the male when singing is always with the head upward. 

 The abdomen is then elevated and apparently inflated, and 

 with the beginning of the sound is slowly brought down 

 against the limb, when the note ceases. After a rest of a 

 few seconds this operation is repeated. These abdominal 

 movements vary in different species of cicada and determine 

 in a measure the peculiar notes of each." Each species has 

 a distinctive note, so that anyone used to the song of these 

 insects can at once recognise their note as we can recognise 

 the song of certain birds. 



The ovipositor (fig. 9), as its name implies, is the organ 

 for depositing eggs ; but in the periodical cicada it serves 

 another purpose as well it is a boring organ, for the eggs 

 are always laid in the twigs and younger shoots of trees. 

 When at rest, this organ is almost concealed by the over- 

 lapping sides of the eighth abdominal segment ; it is also 

 protected by two valves, which form a sort of sheath or 

 scabbard. Within this sheath is the ovipositor proper, a 

 very tough, spear-shaped instrument serrated at the ex- 

 tremity, and consisting of three pieces, also a back portion 

 which acts as a support for the lateral blades. These blades 

 slide up and down, alternately, on tongues projecting from 



