136 iv. 13. 



Fishes, unless, like the Batos^ and the Trygon, they are broad 

 and flat, have four fins, two on the upper and two on the under 

 aspect of the body ; and no fish ever has more than these. For, 

 if it had, it would be an ex-sanguineous animal. 



The upper pair of fins is present in nearly all fishes, but not so 

 the under pair; for these are wanting in some of those fishes 

 that have long thick bodies, such as the eel, the conger, and the 

 Cestreus which is found in the lake at Siphae.^" When the body 

 is still more elongated, and resembles that of a serpent rather than 

 that of a fish, as is the case in the Smyraena,^^ there are absolutely 

 no fins at all; and locomotion ^^ is effected by the flexures of the 

 body, the water being put to the same use by these fishes as is 

 the ground by serpents. For in fact serpents swim in water 

 exactly in the same way as they glide on the ground. The reason 

 for these serpent-like fishes being without fins is precisely the 

 same as that which causes serpents to be without feet ; and what 

 this is has been already stated in the dissertation on the Pro- 

 gression and the Motion of Animals.'^ The reason was this. If 

 the points of motion were four,^* motion would be effected under 

 difficulties. For either the two pairs of fins would be near each 

 other, in which case motion would scarcely be possible, or they 

 would be at a very considerable distance apart, in which case the 

 long interval between them would be just as great an evil. On the 

 other hand, to have more than four such motor points is out of 

 the question. For that would convert the fishes into ex-sanguineous 

 animals.^^ A similar explanation applies to the case of those 

 fishes that have only two fins. For here again the body is of 

 great length and like that of a serpent, and its undulations do 

 the office of the two missing fins. It is owing to this that such 

 fishes can even crawl on dry ground, and can live there for a 

 considerable time; and do not, like other fishes, begin to gasp 

 the moment they are taken out of the water ; and the less so, the 

 nearer their nature conforms to that of land-animals. In such 

 fishes as have but two fins it is the upper pair that is present, ^^ 

 excepting when the flat broad shape of the body prevents this. 

 These fins, moreover, in such cases are placed at the head, because 

 in. this region there is no elongation, which might serve in the 

 absence of fins as a means of locomotion ; whereas in the 

 direction of the tail there is a considerable lengthening out in 

 fishes of this conformation. As for the Bati and the like, they 

 696 a. 



