138 iv. 13. 



but few gills, and those of corhparatively small efficacy, can live 

 out of water for a considerable time ; for in them there is no great 

 demand for refrigeration. Such, for example, are the eel and all 

 other fishes of serpent-like form.^^ 



Fishes also present diversities as regards the mouth. In some 

 this is placed in front, at the very extremity of the body, while 

 in others, as the dolphin ^s and such fishes as resemble the Selachia, 

 it is placed on the under surface ; so that these fishes have to turn 

 on their backs in order to take their food. The purpose of nature 

 in this was apparently not merely to provide a means of salvation 

 for other animals, by allowing them opportunity of escape during 

 the time lost in the act of turning — for all the fishes with this kind 

 of mouth prey on living animals — but also to prevent these fishes 

 from giving way too much to their gluttonous ravening after food.^^ 

 For had they been able to seize their prey more easily than they 

 do, they would soon have perished from over-repletion. An 

 additional reason for placing their mouth on the. under surface 

 is that the projecting extremity of the head is round and small, 

 so that a mouth, if placed there, could not possibly open widely. 

 In such fishes as have the mouth placed at the anterior extremity 

 there are differences in the extent to which that orifice can open. 

 In those that are carnivorous, such as the fishes ^° with sharp inter- 

 fitting teeth, whose strength lies in their mouth, this orifice can 

 gape widely, whereas it is placed at the point of a small tapering 

 snout in all such as are not carnivorous. 



The skin is in some fishes covered with scales, a scale being a 

 shiny film which owing to its thinness becomes detached from the 

 surface of the body. In others it is rough, as for instance in the 

 Rhine,^^ the Batos, and the like. In others again, but in very few, 

 the skin is smooth.^^ The Selachia have no scales, but a rough 

 skin. This is explained by their cartilaginous skeleton. For the 

 earthy material which has been thence diverted is expended by 

 nature upon the skin.^^ 



No fish has testicles^* either externally or internally ; as indeed 

 have no apodous animals, among which of course are included 

 the serpents.^^ One and the same orifice serves both for the 

 excrement and for the generative secretions,^^ as is the case also 

 in all other oviparous animals, the quadrupeds as well as the 

 rest, inasmuch as they have no urinary, bladder and form no fluid 

 excretion.^^ 

 697a. 



