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 ............