BOOK IX. VI. 16-18 



creatures in the sea also breathe, those whose 

 internal organs include a lung, since it is thought that 

 no animal is able to breathe without one. Those 

 who hold this opinion beheve that the fishes possess- 

 ing gills do not alternately expire and inspire air, 

 and that many other classes even lacking gills do not 

 — an opinion which I notice that Aristotle " held and 

 supported by many learned researches.* Nor do I 

 pretend that I do not myself immediately accept this 

 view of theirs,'^ since it is possible that animals may 

 also possess other respiratory organs in place of 

 lungs, if nature so wills, just as also many possess 

 another fluid instead of blood. At all events who 

 can be surprised that this hfe-giving breath pene- 

 trates into water if he observes that it is also given 

 back again from the water, and that it also pene- 

 trates into the earth, that much denser element, as is 

 proved by animals that hve always in underground 

 burrows, Hke moles ? Undoubtedly to my mind 

 there ai-e additional facts that make me beheve 

 that in fact all creatures in the water breathe, owing 

 to the condition of their own nature — in the first 

 place a sort of panting that has often been noticed in 

 fishes during the summer heat, and another form of 

 gasping, so to speak, in calm weather, and also the 

 admission in regard to fishes sleeping made even by 

 those persons who are of the opposite opinion — for 

 how can sleep occur without breathing ? — and more- 

 over the bubbles caused on the surface of the water 

 by air rising from below, and the effect of the moon 

 in causing the bodies even of shellfish to increase in 

 size. Above all there is the fact that it ^vill not be 

 doubted that fish have the sense of hearing and smell, 

 both of which are derived from the substance of air : 



175 



