PROGRESSION OF ANIMALS, vi.-vii. 



two things), and, secondly, by the distinction which 

 must arise as soon as there are four things. ° 



Since, then, the superior and the inferior, and the 

 right and the left are connected with one another by 

 the same common origin (and by this I mean that 

 which controls their movement ^), and since in any- 

 thing which is to carry out the movement of each 

 part properly the cause of all the said movements 

 must be somehow defined and arranged at the right 

 distance in relation to the said origins, namely,* 

 those in the limbs, which are in pairs opposite or 

 diagonal to one another,*' (and the cause of their 

 movement is the common origin from which the 

 movement of left and right and likewise of superior 

 and inferior in the animal's limbs is derived), and 

 since this origin must in each animal be at a point 

 where it is in more or less the same relation to each 

 of the origins in the said parts,*^ O'^-''^-'--) it is, therefore, 

 clear that movement from place to place belongs 

 either solely or chiefly to those animals which make 

 their change of place by means of two or four points. 

 And so, since this condition occurs almost exclusively 

 in red-blooded animals, it is clear that no red-blooded 

 animal can move by means of more than four points, 

 and if an animal is so constituted by nature as to 

 move by means of four points only, it must neces- 

 sarily be red-blooded. 



What actually occurs in animals is also in agree- 

 ment with the above statement. For no red-blooded 

 animal can live for any time worth mentioning if it be 



** There are two kinds of dpxai in, e.g., a quadruped, (a) 

 those in each of the four legs and (6) the central dpxv in the 

 heart ; the former must each be approximately equidistant 

 from the latter. 



501 



