GENERATION OF ANIMALS, V. i. 



while as regards their process of forviation, all those 

 characteristics which are contained in its logos, or are 

 subservient to some end, or are an end in themselves 

 — these come to be formed on account of this Cause " 

 as well as the remaining Causes. Other character- 

 istics, however, are formed during the process which 

 do not fall under the headings just given, and the 

 cause of them is to be looked for in the movement, 

 i.e., the process of formation — we must assume that 

 they acquire their differences within the actual pro- 

 cess of construction. Thus (to take an example) 

 X will of necessity possess an eye (because that 

 characteristic ^ is included in the essence of the 

 animal as posited),'' and it will — also of necessity — • 

 possess a particular sort of eye, but the latter is a 

 different mode of necessity' from the former,** and is 

 derived from the fact that it is naturally constituted 

 to act and to be acted upon in this or that way.* 



Having settled these points we may proceed to sleep. 

 those which immediately follow. First then : the 

 habit of the young of all animals, especially those of 

 animals which bring forth their young imperfect, 

 once they have been born, is to sleep, because thev 

 are in fact continually asleep within the parent from 

 the time that they first acquire sensation. There is, 

 however, a puzzle concerning their original forma- 

 tion, which is this : which state exists first in animals, 

 sleep or waking ? From the fact that, as we see, 

 they become more awake the older they get, it seems 

 reasonable to suppose that the opposite state, sleep, 

 is the one that exists at the beginning of their forma- 

 tion — and also from the fact that the transition from 



" %.e., the necessity implied by the Motive and Material 

 Causes. See Introd. § 7. • Cf. App. B §§ 8 flF. 



489 



