One of these ways, viz., when the object is made out of something pre-existing, is exemplified by the formation of a bed out of wood, or a statue from stone ; in which case, the whole material of the future piece of work has already been in existence, before it is finished into form, or any part of the work is yet begun; the second method is, when the material is both made and brought into form at the same time. Just then as the works of art are accomplished in two manners, one, in which the workman cuts the material already prepared, divides it, and rejects what is superfluous, till he leaves it in the desired shape (as is the custom of the statuary) ; the other, as when the potter educes a form out of clay by the addition of parts, or increasing its mass, and giving it a figure, at the same time that he provides the material, which he prepares, adapts, and applies to his work ; (and in this point of view, the form may be said rather to have been made than educed;} so exactly is it with regard to the generation of animals.
Some, out of a material previously concocted, and that has already attained its bulk, receive their forms and transfigura- tions ; and all their parts are fashioned simultaneously, each with its distinctive characteristic, by the process called meta- morphosis, and in this way a perfect animal is at once born ; on the other hand, there are some in which one part is made before another, and then from the same material, afterwards receive at once nutrition, bulk, and form : that is to say, they have some parts made before, some after others, and these are at the same time increased in size and altered in form. The struc- ture of these animals commences from some one part as its nucleus and origin, by the instrumentality of which the rest of the limbs are joined on, and this we say takes place by the method of epigenesis, namely, by degrees, part after part ; and this is, in preference to the other mode, generation properly so called.
In the former of the ways mentioned, the generation of insects is effected where by metamorphosis a worm is born from an egg ; or out of a putrescent material, the drying of a moist substance or the moistening of a dry one, rudiments are created, from which, as from a caterpillar grown to its full size, or from an aurelia, springs a butterfly or fly already of a
