4. In the vital actions also we may observe the same manner. For vegetables which are produced from seed appear to have no other work beyond reproduction; nor do some animals appear to have any other object in their existence. This object then is common to them all; but as sensation advances, their manner of life differs in their having pleasure in sexual intercourse, in their mode of parturition and rearing their young. Some of them, like plants, simply accomplish their peculiar mode of reproduction at an appointed season, and others are diligent in rearing their young; but as soon as this is accomplished they separate from them, and have no farther communication; but those that are more intelligent, and possess more memory, use their offspring in a more civilized manner. 5. The work of reproduction is one part of their life, the work of procuring food forms another. These two occupy their labour and their life. Their food differs in the substances of which it consists, and all the natural increase of the body is derived from food. That which is natural is pleasant, and all animals follow that which is pleasant to their nature. CHAPTER II. 1. Animals are divided according to the localities which they inhabit; for some animals are terrestrial, others are aquatic. They also admit of a ternary division, those that breathe air and those that breathe water, one of these classes is terrestrial, the other is aquatic; the third class does not breathe either air or water, but they are adapted by nature to receive refreshment from each of these elements; and some of these are called terrestrial, others are aquatic, though they neither breathe air or water; and there are other animals which procure their food and make their abode in either of these elements. For many that breathe air, and produce their young upon the land, procure their food from the water, where they generally make their abode; and these are the only animals which appear to be doubtful, for they may be arranged either as terrestrial or aquatic animals. 2. Of those that breathe water, none have feet or wings, nor seek their food on land; but many of those that are terrestrial, and breathe air, do so; some of them so much so, that they cannot live when separated from the water, as those which are called marine turtles, and crocodiles, and hippopotami, and seals, and some of the smaller creatures, as the water tortoise and the frog tribe; for all these are suffocated if their respiration is suspended for any length of time. They produce their young and rear them on dry land; others do so near the dry land, while they reside in the water.