PROGRESSION OF ANIMALS, v.-vi. 



that, because the origins are situated in these parts, 

 they are therefore more honourable than the opposite 

 parts. 



VI. It is clear, then, from what has been said that 

 the origin of movement is on the right. Now in 

 anything continuous of which part is in motion and 

 part at rest (the whole being able to move while one 

 part stands still), there must be, at the point where 

 both parts move in opposite movements, something 

 common to both which makes these parts continuous 

 with one another (and at this point must be situated 

 the origin of the movement of each of these parts, 

 and likewise also of their immobility) : it is evident, 

 therefore, that in respect of whichever of the above- 

 mentioned contraries" the individual movement of 

 each of the opposite parts takes place, there is in 

 all these cases a common origin of movement by 

 reason of the interconnexion of the said parts, namely, 

 of the right and the left, the superior and the inferior, 

 the front and the back. The differentiation accord- 

 ing to front and back is not one which applies to 

 that which moves itself, because nothing possesses a 

 natural movement backwards nor has the moving 

 animal any distinction in accordance with which it 

 can make a change from place to place in each of 

 these two directions ^ ; but there is a differentiation 

 of right and left, superior and inferior. All animals, 

 therefore, which progress by the employment of in- 

 strumental parts have these parts differentiated, not 

 by the distinction between front and back, but by the 

 other two pairs, first, by the distinction of right and 

 left (for this must immediately exist where there are 



^ In other words an animal cannot divide itself into two 

 parts, one of which goes forwards and the other backwards. 



499 



