Chapter IV.

1. There are also viviparous, oviparous, and vermiparous animals. The viviparous, are such as man, and the horse, the seal, and others which have hair, and among marine animals the cetacea, as the dolphin and those which are called selache.[16] Some of these are furnished with a blow-hole, but have no gills, as the dolphin and the whale. The dolphin has its blow-hole on the back, the whale in its forehead; others have open gills, as the selache, the galeus,[17] and the batus.[18] That is called the egg of the perfect fœtus, from which the future animal is produced, from a part at first, while the remainder serves for its food. The worm is that from the whole of which the future animal is produced, and the fœtus afterwards acquires parts and increases in size.

2. Some viviparous animals are internally oviparous, as the selache; others are internally viviparous, as mankind and the horse. In different animals the fœtus assumes a different form, when first brought into the world, and is either a living creature, an egg, or a worm. The eggs of some animals, as birds, are hard-shelled, and are of two colours. Those of the selache and some other animals are soft-skinned, and have only one colour. Some species of the vermiform fœtus are capable of motion, others are not. But in another place, when we treat of generation, we will dwell more accurately on these subjects.