ON GENERATION. 337 



which, in the course of growth, has at one and the same time dis- 

 tinct structures formed and its figure established, and acquires an 

 additional birth of parts afterwards, each in its own order ; in 

 the same way, for instance, as the bud bursting from the top of 

 the acorn, in the course of its growth, has its parts separately 

 taking the form of root, wood, pith, bark, boughs, branches, 

 leaves, flowers, and fruit, until at length out comes a perfect 

 tree ; just so is it with the creation of the chick in the egg : 

 the little cicatrix, or small spot, the foundation of the future 

 structure, grows into the eye and is at the same time sepa- 

 rated into the colliquament ; in the centre of which the 

 punctum sanguineum pulsans commences its being, together 

 with the ramification of the veins ; to these is presently added 

 the nebula, and the first concretion of the future body; this 

 also, in proportion as its bulk increases, is gradually divided 

 and distinguished into parts, which however do not all emerge 

 at the same time, but one after the other, and each in its 

 proper order. To conclude, then : in the generation of those 

 animals which are created by epigenesis, and are formed in 

 parts, (as the chick in the egg,) we need not seek one material 

 for the incorporation of the foetus, another for its commencing 

 nutrition and growth ; for it receives such nutrition and growth 

 from the same material out of which it is made ; and, vice versa, 

 the chick in the egg is constituted out of the materials of its 

 nutrition and growth. And an animal which is capable of 

 nutrition is of the same potency as one which is augmenta- 

 tive, as we shall afterwards show; and they differ only, as 

 Aristotle says, in their distinctness of being; in all other respects 

 they are alike. For, in so far as anything is convertible into a sub- 

 stance, it is nutritious, and under certain conditions it is augmen- 

 tative : in virtue of its repairing a loss of substance, it is called 

 nutriment, in virtue of its being added, where there is no such 

 loss of substance, it is called increment. Now the material of 

 the chick, in the processes of generation, nutrition, and aug- 

 mentation is equally to be considered as aliment and incre- 

 ment. We say simply that anything is generated, when no 

 part of it has pre-existed; we speak of its being nourished and 

 growing when it has already existed. The part of the foetus 

 which is first formed is said to be begotten or born ; all sub- 

 stitutions or additions are called adnascent, or aggenerate. 



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