Belonging also to the class of shell-fish is the dactylus,[1] a fish so called from its strong resemblance to the human nails. It is the property of these fish to shine brightly in the dark, when all other lights are removed, and the more moisture they have, the brighter is the light they emit. In the mouth even, while they are being eaten, they give forth their light, and the same too when in the hands; the very drops, in fact, that fall from them on the ground, or on the clothes, are of the same nature. Hence it is beyond a doubt, that it is a liquid that possesses this peculiar property, which, even in a solid body, would be a ground for considerable surprise.