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 breathe, but when the latter are breathing 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 breathing); while in creatures which do not breathe 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