MEANS OF DEFENCE OF INSECTS. 245 
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, L., as also 
P. Apollo and many other Lquites?.—Another insect, the 
larva of a species of saw-fly (Tenthredo) described by De 
Geer, is furnished with osmateria, or scent-organs, of a 
different kind. They are situated betwen 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they are withdrawn within the body®.—The grub of the 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 Populz, L.) also is remark- 
able 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 
milky fluid, the smell of which, De Geer observes, is almost 
insupportable, being inexpressibly strong and penetrating. 
These drops proceed at the same instant from all the 
eighteen scent-organs; which forms a curious spectacle. 
The insect, however, does not waste this precious fluid : 
each drop instead of falling, after appearing for a moment 
and dispensing its perfume, is withdrawn again within 
@ Merian Surinam. 17. Jonesin Linn. Trans. u. 64, 
» De Geer, ii, 989— ¢. xxxvii.f. 6. 
