Chapter I.

1. We have hitherto treated of the external and internal parts of all animals, of their senses, voice, and sleep, with the distinctions between the males and females; it remains to treat of their generation, speaking first of those which come first in order, for they are many, and have numerous varieties, partly dissimilar, and partly like each other. And we will pursue the same order in considering them as we did before in their division into classes; we commenced our consideration by treating of the parts in man, but now he must be treated of last, because he is much more intricate.

2. We shall begin with the testacea, and after these treat of the malacostraca, and the others in the order of their succession. These are the malacia and insects, next to these fishes, both viviparous and oviparous; next to them birds, and afterwards we must treat of animals with feet, whether viviparous or oviparous; some viviparous creatures have four feet, man alone has two feet. The nature of animals and vegetables is similar, for some are produced from the seed of other plants, and others are of spontaneous growth, being derived from some origin of a similar nature. Some of them acquire their nourishment from the soil, others from different plants, as it was observed when treating of plants.

3. So also some animals are produced from animals of a similar form, the origin of others is spontaneous, and not from similar forms; from these and from plants are divided those which spring from putrid matter, this is the case with many insects; others originate in the animals themselves, and from the excrementitious matter in their parts; those which originate from similar animals, and have both the sexes are produced from coition, but of the class of fishes there are some neither male nor female, these belong to the same class among fishes, but to different genera, and some are quite peculiar. In some there are females but no males, by these the species is continued as in the hypenemia among birds.

4. All these among birds are barren, (for nature is able to complete them as far as the formation of an egg,) unless persons suppose that there is another method of communicating the male influence, concerning which we shall speak more plainly hereafter. In some fish, after the spontaneous production of the ovum, it happens that living creatures are produced, some by themselves, others by the aid of the male. The manner in which this is done will be made plain in a future place, for nearly the same things take place in the class of birds.

5. Whatever are produced spontaneously in living creatures, in the earth, or in plants, or in any part of them, have a distinction in the sexes, and by the union of the sexes something is produced, not the same in any respect, but an imperfect animal, as nits are produced from lice, and from flies and butterflies are produced egg-like worms, from which neither similar creatures are produced, nor any other creature, but such things only. First of all, then, we will treat of coition, and of the animals that copulate, and then of others, and successively of that which is peculiar to each, and that which is common to them all.