IV. 13— IV. 14- 139 



Such then are the characters which distinguish fishes from all 

 other animals. But dolphins and whales and all such Cetacea^® 

 are without gills ; and, having a lung, are provided with a blow- 

 hole. By this they discharge the sea-water which has been taken 

 into the mouth.^^ For, feeding as they do in the water, they 

 cannot but let this fluid enter into their mouth, and, having let 

 it in, they must of necessity let it out again. This they cannot 

 do by the aid of gills ; for the use of gills, as has been explained 

 in the treatise on Respiration, is limited to such animals as do 

 not breathe ; so that no animal can possibly possess gills and 

 at the same time be a respiratory animal.^** In order, therefore, 

 that these Cetacea may discharge the water, they are provided 

 with a blow-hole. This is placed in front of the brain ; for, if 

 placed behind, it would have cut off the brain from the spine.'*^ 

 The reason for these animals having a lung and breathing, is 

 that their large size demands an excess of heat, to render motion 

 possible.'*^ A lung, therefore, is placed within their body, and is 

 fully supplied with blood-heat. These creatures are after a fashion 

 land and water animals in one. For so far as they are inhalers 

 of air they resemble land-animals, while they resemble water- 

 animals in having no feet and in deriving their food from the 

 sea. So also seals *^ lie half-way between land and water animals, 

 and bats half-way between animals that live on the ground and 

 animals that fly ; and so may be said to belong to both kinds 

 or to neither. For seals, if looked on as water-animals, are yet 

 found to have feet ; and, if looked on as land-animals, are yet 

 found to have fins. For their hind feet are exactly like the fins 

 of fishes. Their teeth also are all of the sharp and interfitting 

 kind, as in fishes.'** Bats again, if regarded as winged animals, 

 have feet ; and, if regarded as quadrupeds, are without them.'*^ 

 So also they have neither the tail of a quadruped nor the tail of 

 a bird ; no quadruped's tail, because they are winged animals ; 

 no bird's tail, because they live on the ground. This absence 

 of tail is the result of necessity. For bats fly by means of a 

 membrane, not by means of barbed feathers ; and no animal 

 unless it has barbed feathers has the tail of a bird ; for a bird's 

 tail is composed of such barbed feathers. As for a quadruped's 

 tail, it would be an impediment to an animal that flies. 



(Ch. 14.J Much the same may be said also of the Libyan ostrich. 

 For it has some of the characters of a bird, some of the characters 

 697b. 



