MEANS OF DEFENCE OF INSECTS. 245 



niarkable. If you press the abdomen hard, you will 

 find that these vesicles are only branches from a com- 

 mon stem ; and you may easily ascertain that the smell 

 of this insect, which mixes something 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 caterpillar of 

 the swallow-tail butterfly {Fapilio Machoon^ lu.Y. 

 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 ilies and ichneumons that annoy it. 

 A similar horn is protruded by the slimy larva of 

 P. ylnchises, L., as also P. Apollo and many other 

 EquUes^'. — Another insect, the larva of a species of 

 saw-ily (Tent/iredo) described by De Geer, is furnished 

 with osmateria, or scent-organs, of a different kind. 

 They are situated between the five first pair of in- 

 termediate 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 tlie horns of 

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

 long upon the linger ; but when the pressure is re* 

 moved they are withdrawn within the body*^. — The 

 grub of the poplar-beetle {Chri/somela Populi, L.) 

 also is remarkable for similar organs. On each of the 

 iiine intermediate dorsal segments of its body is a paii? 



* PtATE XIX. Fig. 1. a. " Mcrian S-urinam. 17- Jones in Linn, 



Trans, ii. Gt. <= De Geer, ii. 969— i, xxxvii./. 6, 



