The strange association of ideas that we have seen in many other instances may be well seen again in the notion that if one pounds up those luminous creatures of the night, glowworms, the result will be an ink that will render any writing performed by its aid visible in the dark. Winstanley, in his “Pathway to Knowledge,” gives a simple receipt for the manufacture of this useful ink, and other writers are content to copy him, or each other, in the laudable desire to spread abroad the knowledge of this luminous fluid. One can easily realize that such a preparation might at times be really very useful. Turning, in conclusion, our attention to the creatures of sea and stream, we at once encounter the favourite mediæval theory that all creatures of the land had their marine counterparts. “There is nothing,” says the comparatively modern writer, Camden, “bred in any part of Nature, but the same is in the sea;” while Olaus Magnus affirms that “there be fishes like to dogs, cows, calves, horses, eagles, dragons, and what not.” These mysterious denizens of the deep were an unfailing resource in the romances and poems of the Middle Ages, and an article of faith with the writers on natural history. On the Assyrian slabs we see the monster “upward man and downward fish,” while the mermaid we all recognize as a most familiar instance of the presence of creatures at least semi-human in the broad and mysterious expanse of ocean. Bœwulf, the Saxon poet, writes of “the sea-wolf of the abyss, the mighty sea-woman.” The quotation is not altogether complimentary in its sentiment: no lady of one’s acquaintance would feel flattered on being addressed as a sea-wolf. But while a certain halo of romance has in these later days gathered round the idea of the mermaid, those who really believed in her gave her credit for deeds considerably more heinous than combing her flowing hair in the sunlight, since her beauty was a snare and destruction to all who came within its fatal influence.