PARTS OF ANIMALS, IV. xiii. 



either be very close together, or else a long way apart, 

 and in either case would not move easily. (6) On the 

 other hand, if they had more than four motion-points 

 they would be bloodless creatures. The same reason 

 holds good for those fishes that have only two fins. 

 These also are serpent-like and fairly long, and they 

 use their power of bending instead of the two missing 

 fins. And this enables them besides to crawl about 

 and to live a good length of time on dry land ; and 

 it is some while before they begin to gasp ; indeed, 

 those which are akin to the land-animals are affected 

 even less than the others. 



Except for those whose width and flatness prevents 

 it, all fishes that have only two fins have the upper * 

 ones ; and these fins are by the head, because there 

 is no length of body just there which they could use 

 instead of fins for propulsion — length such as fish 

 of this sort have towards their tail-end. The Batoi 

 and such fishes swim by means of the edge of their 

 flat surface Mhich they use instead of fins. Fish 

 which are not so flat, such as the torpedo-fish and the 

 fishing-frog, possess fins, but they have their upper 

 fins toward their tail-end owing to the flatness of 

 the forepart, and their under fins near the head (since 

 the flatness of the fish does not prevent its motion) ; 

 but the under ones are smaller than the upper ones, 

 to make up for being placed forward. The torpedo- 

 fish has two of his fins by his tail ; and instead of 

 these two he uses the wide piece on each of his semi- 

 circles ^ as though it were a fin. 



We have already spoken of the parts in the head 

 and of the sense-organs. 



" i.e. pectoral. 

 * Cf. De incessu an. 709 b 17, 



421 



