82 OF THE SENSES OF 
passed over it was sure to visit the blossoms of an 
Alpine blue nettle, (the Centawrea montanea.) This 
is the more remarkable, as that flower is known to 
have but little effect on the olfactory nerves of the 
human species. Now, these butterflies were alive to 
its odour at upwards of twenty feet. This fact is the 
more striking, as the odours of flowers are said by 
M. Le Chat to be much heavier than atmospheric 
air, and therefore but seldom rise in it. We have 
ascertained this to be true, from the circumstance, 
that mignionette, although possessing a powerful 
odour, and planted close to a building, can be but 
faintly, if at all, perceived from a window one story 
high ; although, on going to the surface of the earth, 
we find the atmosphere surcharged with its fragrance 
at the distance even of from fifty to an hundred 
yards. Mr Rennie remarked that even the Painted 
Lady Butterfly, (Cynthia cardui,) which always 
flies at a considerable height, alighted on the plants 
above mentioned, thus proving that their perception 
of odours is very acute. 
It is a practice with collectors to entrap the large 
Tortoise-shell Butterfly, (Vanessa polychlorus,) by 
spreading honey on the leaves of a tree which they 
are in the habit of frequenting. 
There is great difficulty in determining by what 
means the organ of smell in insects manifests itself ; 
for, as they do not breathe like quadrupeds, or other 
warm-blooded animals, by the mouth, but by an in- 
