On Sense And The Sensible   

needless creation of two organs of sense; for in the fact that they

respire the other animals have already sufficient provision for

their perception of the one species of odour only, as human beings

have for their perception of both.

But that creatures which do not respire have the olfactory sense

is evident. For fishes, and all insects as a class, have, thanks to

the species of odour correlated with nutrition, a keen olfactory sense

of their proper food from a distance, even when they are very far away

from it; such is the case with bees, and also with the class of

small ants, which some denominate knipes. Among marine animals, too,

the murex and many other similar animals have an acute perception of

their food by its odour.

It is not equally certain what the organ is whereby they so

perceive. This question, of the organ whereby they perceive odour, may

well cause a difficulty, if we assume that smelling takes place in

animals only while respiring (for that this is the fact is manifest in

all the animals which do respire), whereas none of those just

mentioned respires, and yet they have the sense of smell- unless,

indeed, they have some other sense not included in the ordinary

five. This supposition is, however, impossible. For any sense which

perceives odour is a sense of smell, and this they do perceive, though

probably not in the same way as creatures which respire, but when

the latter are respiring the current of breath removes something

that is laid like a lid upon the organ proper (which explains why they

do not perceive odours when not respiring); while in creatures which

do not respire this is always off: just as some animals have eyelids

on their eyes, and when these are not raised they cannot see,

whereas hard-eyed animals have no lids, and consequently do not

need, besides eyes, an agency to raise the lids, but see straightway

[without intermission] from the actual moment at which it is first

possible for them to do so [i.e. from the moment when an object

first comes within their field of vision].