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. 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
close to 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
would convert the fishes into bloodless 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 begin to gasp until they
have been for a considerable time out of the water, while others,
whose nature is akin to that of land-animals, do not even do as much
as that. In such fishes as have but two fins it is the upper pair
(pectorals) that is present, excepting when the flat broad shape of
the body prevents this. The fins 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 use the marginal
part of their flattened bodies in place of fins for swimming
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