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 protruded by the slimy larva of P. Anchises, as also 

 Parnassius Apollo and many other Equites b . 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 they are withdrawn within the body c . The grub of the 

 poplar-beetle (Chrysomela Populi] also is remarkable 

 for similar organs. 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 



a PLATE XIX. FIG. 1. a. 



b Merian Surinam. } 7. Jones in Linn. Trans, ii. 64. 



c De Geer, ii. 989*. xxxvii. /. 6. 



