IV. 12 — IV. 13- 135 



as has been described, in all birds with one exception. This 

 exception is the wryneck.^ Here two of the toes are in front, 

 the other two behind ; and the reason for this is that the body 

 of the wryneck is not inclined forwards so much as that of other 

 birds. All birds have testicles ; but they are inside the body. 

 The reason for this will be given in the treatise on the Generation 

 and Development of Animals.'* 



(Ch. 13.J Thus then are fashioned the parts of birds. But in 

 fishes^ a still further stunting has occurred in the external parts. 

 For here, for reasons already given,^ there are neither arms nor 

 legs nor wings, the whole body from head to tail presenting one 

 unbroken surface. This tail differs in different fishes, in some 

 having a consistency similar to that of the body, while in others, 

 namely in some of the flat kinds, it is spinous and elongated, 

 because the material which should have gone to the tail has been 

 diverted thence and used to increase the breadth of the body. 

 Such for instance is the case with the Torpedos,' the Trygons,* and 

 whatever other Selachia there may be of like nature. In such 

 fishes, then, the tail is spinous and long ; while in some others 

 it is short and fleshy, for the very same reason which makes it 

 spinous and long in the Torpedo. For to be short and fleshy 

 comes to exactly the same thing as to be long and less amply 

 furnished with flesh. 



What has occurred in the Fishing-frog,^ is exactly the reverse 

 of what has occurred in the other instances just given. For here 

 the anterior and broad part of the body is destitute of flesh, and 

 so all the fleshy substance which has been thence diverted has 

 been placed by nature in the tail and hinder portion of the body. 



In fishes there are no limbs attached to the body. For in 

 accordance with their essential constitution they are swimming 

 animals ; and nature never makes anything superfluous or void of 

 use. Now, seeing that fishes are essentially sanguineous animals, 

 they must have four points of motion ; and, seeing that they are 

 meant for swimming, these must be fin& and not feet; for feet 

 are attached to the body that they may be of use in walking on 

 dry ground.^ Moreover it is impossible for fishes, that are san- 

 guineous animals, to have four fins and also at the same time, to 

 have feet or in fact any other kind of limb. Tadpoles,' it is 

 true, though they have gills, have feet; but then they have no 

 fins, but merely have their tail flattened out and loose in texture.* 

 695 b. 



