(C ‘Esti7) 
organs of smell is still doubtful. One point, however, is 
clear, namely, that if the organs I have alluded to are really 
for olfactory purposes, their functions must be exercised in 
a very different way from that in which we smell. For 
instance, it is difficult to imagine that any sense of smell can 
exist without the passage of air over the sensitive surface, for 
the minute particles of some odorous substances must be 
extremely rare; hence, as there is in ordinary circumstances 
no such current of air in contact with the antenne of insects, 
it would seem that their functions in many cases can only be 
exercised fully when the insect is moving rapidly through the 
air: at least so far as contact with odorous particles goes it 
could be effected in this manner; so that we are brought to 
the strange conclusion that an insect may smell acutely when 
it is flyimg through the air, and be unable to perceive the 
Same odours when it is quiescent. In another respect the 
insect antenne may be superior to our olfactory organs, for 
these latter can only smell odorous substances when these 
are in a dynamical state, that is when their particles are being 
or have been recently dispersed ; but it is quite conceivable, 
nay probable, that many substances only disperse their odorous 
particles under certain circumstances, and yet the odorous 
particles are there ; well, in such a case it is possible that the 
insect can still perceive the smell, though to us there is 
none, for the insect can go to the object and lay its olfactory 
organ on the quiescent odours and so detect them. But I 
must not detain you by speaking at greater length on this 
point. The knowledge of insect olfactory organs is even 
more primitive and uncertain than that of their optic 
organs, and you will therefore readily understand that im- 
proved knowledge on this point may quite change our views 
as to some of the phenomena of insect life. 
In regard to the other senses I must content myself with 
the assertion that we know very little about them. The 
sense of touch insects can scarcely be considered to possess 
at all, owing to the fact that their skeleton is external ; 
nevertheless these creatures undoubtedly receive some tactile 
impressions by means of sete, or structures approximating to 
setze, whose bases pass more or less completely through the 
