242 MEANS OF DEFENCE OF INSECTS. 



only branches from a common stem; and you may easily 

 ascertain that the smell of this insect, which mixes some- 

 thing extremely fetid with a spicy odour, proceeds from 

 their extremity. — A similar organ, half an inch in length, 

 and of the same shape, issues from the neck of the cater- 

 pillar of the swallow-tail-butterfly [Papilio Machaon)*-. 

 When I pressed this caterpillar, says Bonnet, near its^ 

 anterior part, it darted forth its horn as if it meant to 

 prick me with it, directing it towards my fingers ; but it 

 withdrew it as soon as I left off pressing it. ^This horn 

 smells strongly of fennel, and probably is employed by 

 the insect, by means of its powerful scent, to drive away 

 the flies and ichneumons that annoy it. A similar horn 

 is pi'otruded by the slimy larva of P. A?ichises, as also 

 Parnassius Apollo and many other Equites^. — Another 

 insect, the larva of a species of saw-fly described by De 

 Geer, is furnished with osmateria, or scent-organs, of a 

 different kind. They are situated between the five first 

 pair of intermediate legs, which they exceed in size, and 

 are perforated at the end like the rose of a watering-pot. 

 If you touch the insect, they shoot out like the horns of 

 a snail, and emit a most nauseous odour, which remains 

 long upon the finger; but when the pressure is removed 

 they are withdrawn within the body*^. — The grub of the 

 poplar-beetle [Chrysomela Populi) also is remarkable 

 for similar oro-ans. On each of the nine intermediate 

 dorsal segments of its body is a pair of black, elevated, 

 conical tubercles, of a hard substance ; from all of these 

 when touched the animal emits a small drop of a white 



" PlateXIX. Fig. l.a. 



"^ Merian Surinam. IT- Jones in L'mn. Trans, ii. G4. 



•^ De Geer, ii. 989— /. xxxvii. /. 0. 



