MEANS OF DEFENCE OF INSECTS. 



199 



from them ; and, perhaps, some in the list produce it from 

 particular organs not yet noticed. 



I shall next beg your attention to those insects that emit 

 their smell from particular organs. Of these, some are fur- 

 nished with a kind of scent-vessels, which I shall call osma- 

 teria; while in others it issues from the intestines at the 

 ordinary passage. In the former instance the organ is usually 

 retractile within the body, being only exserted when it is used : 

 it is generally a bifid vessel, something in the shape of the 

 letter Y. Linne, in his generic character of the rove-beetles 

 (Staphylinidce), mentions two oblong vesicles as proper to this 

 genus. These organs, — which are by no means common to 

 the whole genus, even as restricted by late writers, — are its 

 osmateria, and give forth the scent for which some species, 

 particularly Ocypus brunnipes, are remarkable. If you press 

 the abdomen hard, you will find that these vesicles are only 

 branches from a common 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-but- 

 terfly {Paj)ilio 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 oif 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 and many other 

 JEquites 1 , as also Parnassius Apollo. 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 situ- 

 ated between the first five 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 re- 



1 Merian Surinam, 17. Jones in Linn. Trans, ii. 64. 



o 4 



