CHAPTER XIII. BODIES WHICH HAVE A THIRD NATURE, THAT OF THE ANIMAL AND VEGETABLE COMBINED. For my own part, I am strongly of opinion that there is sense existing in those bodies which have the nature of neither animals nor vegetables, but a third which partakes of them both:—sea-nettles and sponges, I mean. The sea-nettle wanders to and fro by night, and at night changes its locality. These creatures are by nature a sort of fleshy branch, and are nurtured upon flesh. They have the power of producing a smarting pain, just like that caused by the nettle found on land. For the purpose of seeking its prey, it contracts and stiffens itself to the utmost possible extent, and then, as a small fish swims past, it will suddenly spread out its branches, and so seize and devour it. At another time it will assume the appearance of being quite withered away, and let itself be tossed to and fro by the waves like a piece of sea-weed, until it happens to touch a fish. The moment it does so, the fish goes to rub itself against a rock, to get rid of the itching; immediately upon which, the nettle pounces upon it. By night also it is on the look-out for scallops and sea-urchins. When it perceives a hand approaching it, it instantly changes its color, and contracts itself; when touched it produces a burning sensation, and if ever so short a time is afforded, makes its escape. Sponges grow on rocks, and feed upon shell- and other fish, and slime. It would appear that these creatures, too, have some intelligence; for as soon as they feel the hand about to tear them off, they contract themselves, and are separated with much greater difficulty: they do the same also when the waves buffet them to and fro. About Torone it is said that they will survive after they have been detached, and that they grow again from the roots which have been left adhering to the rock. They leave a color like blood upon the rock from which they have been detached, especially those which are produced in the Syrtes of Africa.