And now it is that the rudiments of the embryo first become conspicuous, as may be seen in the fifth and sixth figure of Fabricius; the egg being put into fair water it will be easy to perceive what parts of the body are formed, what are still wanting. The embryo now presents itself in the form of a small worm or maggot, such as we encounter on the leaves of trees, in spots of their bark, in fruit, flowers, and elsewhere; but especially in the apples of the oak, in the centre of which, surrounded with a case, a limpid fluid is contained, which, gradually inspissated and congealed, acquires a most delicate outline, and finally assumes the form of a maggot; for some time, however, it remains motionless; but by and by, endowed with motion and sensation it becomes an animal, and subsequently it breaks forth and takes its flight as a fly. Aristotle ascribes a similar mode of production to those creatures that are spontaneously engendered.[187] “Some are engendered of the dew,” he says, “which falls upon the leaves.” And by and by he adds, “butterflies are engendered from caterpillars, but these, in their turn, spring from green leaves, particularly that species of raphanus which is called cabbage. They are smaller than millet seeds at first, and then they grow into little worms; next, in the course of three days into caterpillars; after which they cease from motion, change their shape, and pass into chrysalides, when they are inclosed in a hard shell; although, if touched, they will still move. The shell after a long time cracks and gives way, and the winged animal, which we call a butterfly, emerges.” But our doctrine--and we shall prove it by and by--is, that all animal generation is effected in the same way; that all animals, even the most perfect, are produced from worms; a fact which Aristotle himself seems to have noted when he says: “In all, nevertheless, even those that lay perfect eggs, the first conception grows whilst it is yet invisible; and this, too, is the nature of the worm.”[188] For there is this difference between the generation of worms and of other animals, that the former acquire dimensions before they have any definite form or are distinguished into parts, in conformity with what the philosopher[189] says in the following sentence: “An animal is fashioned from an entire worm, not from any one particular part, as in the case of an egg, but the whole increases and becomes an articulated animal,” i. e. in its growth it separates into parts. It is indeed matter worthy of admiration, that the rudiments of all animals, particularly those possessed of red blood, such as the dog, horse, deer, ox, common fowl, snake, and even man himself, should so signally resemble a maggot in figure and consistence, that with the eye you can perceive no difference between them.