PROGRESSION OF ANIMALS, x. 



legs were taken from them, or walk if their wings 

 were taken from them, just as a man cannot walk 

 without moving his shoulders to some extent. All 

 things, as has been said, make their change of position 

 by bending and stretching ; for they all progress 

 upon that which, being beneath them, also as it were 

 gives way to them up to a certain point ; so that, 

 even if the bending does not take place in any other 

 part, it must at any rate do so at the point where the 

 wing begins in flying insects ^ and in birds, and where 

 the analogous part begins in other animals, such as 

 fishes. In other animals, snakes for example, the 

 beginning of their bending is in the joints of the body. 

 In winged creatures the tail is used, like the rudder 

 in a ship, to direct the flight ; and this too must bend 

 at the point where it joins the body. Flying insects 

 also, therefore, and those birds ^ whose tails are ill- 

 adapted for the purpose just mentioned, peacocks, 

 for example, and domestic fowls and, generally, those 

 birds which are not adapted for flight, cannot keep 

 a straight course. Of the flying insects not a single 

 one possesses a tail, so that they are carried along 

 like rudderless ships and collide with anything that 

 they happen to meet. The same is true of sheath- 

 winged insects,'' such as beetles and cockchafers, 

 and the sheathless insects, such as bees and wasps. 

 The tail is useless in such birds as are not adapted 

 to flight, the porphyrio,*^ for example, and the heron 

 and water-fowls in general ; these fly stretching out 



" Coleoptera. 



<* The identity of this bird is disputed. W. W. Merry (on 

 Aristoph. Aves, 707) suggests some kind of coot ; D'A. W. 

 Thompson (on H.A. 509 a 11, 595 a 13) suggests the purple 

 coot or the flamingo. 



517 



