is impossible in the present state of our knowledge to say. Anatomically the end-organ of fishes is simpler, but there are some species, the dog-fishes for example, which possess a large olfactory lobe in the brain; and this certainly suggests that they, at all events, are gifted with an olfactory sense of relatively high development.
Experiment on fish is difficult, nevertheless it has been definitely proved that they do smell, and it seems probable that the sense is used by them for food-perception. Moreover, that it may be highly sensitive seems likely from the fact that sharks (which belong to the same order as dog-fish) can be attracted from great distances to putrid meat thrown into the water as bait, the high dilution of which resembles the behaviour of odour in an air medium.
The belief that life in water, however, is less favourable than life on land to the fullest development of the sense is supported by the fact we have already mentioned that mammals living in water are extremely microsmatic.
In the macrosmatic terrestrial animals not only is the olfactory sense relatively highly organised, but it is absolutely the predominant sense. Vision is subsidiary to it. In their brains the olfactory region constitutes by far the largest component.
(The same, by the way, is true of the Reptilia.)
