ON GENERATION. 411 



tion of the blood,) urging the blood in a ceaseless round through 

 every part of the body, we see that the blood must exist before 

 the heart, both in the order of generation and of nature and 

 essence. For the blood uses the heart as an instrument, and 

 moreover, when engendered it continues to nourish the organ 

 by means of the coronary arteries, distributing heat, spirits, and 

 life to it through their ramifications. 



We shall have further occasion to show from an entire series 

 of anatomical observations, how this rule of Aristotle in respect 

 of the true priority of the parts is borne out. Meantime we 

 shall see how he himself succeeds in duly inferring the causes 

 of priority in conformity with his rule. 



" After the prime part viz. the heart is engendered/' he 

 says, " the internal parts are produced before the external ones, 

 the superior before the inferior; for the lower parts exist for the 

 sake of the superior, and that they may serve as instruments, 

 after the manner of the seeds of vegetables, which produce roots 

 sooner than branches." 



Nature, however, follows no such order in generation; nor 

 is the instance quoted invariably applicable ; for in beans, peas, 

 and other leguminous seeds, in acorns, also, and in grain, it is 

 easy to see that the stem shoots upwards and the root down- 

 wards from the same germ ; and onions and other bulbous 

 plants send off stalks before they strike root. 



He then subjoins another cause of this order, viz. : " That 

 as nature does nothing in vain or superfluously, it follows that 

 she makes nothing either sooner or later than the use she has 

 for it requires." That is to say, those parts are first engen- 

 dered whose use or function is first required ; and some are 

 begun at an earlier period because a longer time is requisite to 

 bring them to perfection ; and that so they may be in the same 

 state of forwardness at birth as those that are more rapidly 

 produced. Just as the cook, having to dress certain articles 

 for supper, which by reason of their hardness are done with 

 difficulty, or require gentle boiling for a great length of time, 

 these he puts on the first, and only turns subsequently to those 

 that are prepared more quickly and with less expenditure of 

 heat ; and further, as he makes ready the articles that are to 

 come on in the first course first of all, and those that are to be 

 presented in the second course afterwards ; so also does nature 



