GENERATION OF ANIMALS, V. vii. 



amount of air in movement, whereas in the latter the 

 breath is under better control. In every animal, as 

 age advances, this part which sets (the air) in move- 

 ment becomes stronger, so that a change-over" to 

 the opposite is effected : high-pitched voices become 

 deeper than they were, and deep-pitched ones higher. 

 That is why bulls have higher-pitched voices than 

 calves and cows. Now in all animals their strength 

 lies in their sinews, and that actually is why animals 

 in their prime are stronger than the others : young 

 ones are less well articulated and less well supplied 

 with sinews, and furthermore, their sinews have not 

 yet become taut, whereas in ones that are aged their 

 tautness has slackened off. Hence both young and 

 old are weak and powerless so far as producing move- 

 ment is concerned. Bulls however, being especially 

 sinewy, have especially sinewv hearts ; hence this 

 part, by which they set the breath in movement, 

 is taut, just Uke a sinewy string stretched tight. 

 Bull's hearts are shown to be sinewy by the fact 

 that in some of them a bone * actually occurs, and 

 bones seek the nature of sinew. <^ 



All animals when castrated change over to the 

 female state, and as their sinewv* strength is slackened 

 at its source they emit a voice similar to that of 

 females. This slackening may be illustrated in the 

 following way. It is as though you were to stretch a 

 cord and make it taut by hanging some weight on to 

 it, just as women do who weave at the loom ; they 

 stretch the warp by hanging stone weights ^ on to it. 



" For /xeTajSoAAeiv see 766 a 17 ff., 768 a 15 ff. 

 * See also P.A. 666 b 19. 



' This is a literal translation of the Greek. See 744 b 25, 

 36 ff., and Introd. § 64. 



"* Cf. 717 a 35. Lit., " what are called ' laiai ' (stones)." 



549 



