There was, until a year ago, a little and very grimy-looking shop near Seven Dials, over which, in weather-worn yellow lettering, the name of C. Cave, Naturalist and Dealer in Antiquities, was inscribed. The contents of its window were curiously variegated. They comprised some elephant tusks and an imperfect set of chessmen, beads and weapons, a box of eyes, two skulls of tigers and one human, several moth-eaten stuffed monkeys (one holding a lamp), an old-fashioned cabinet, a fly-blown ostrich egg or so, some fishing-tackle, and an extraordinarily dirty, empty glass fish-tank. There was also, at the moment the story begins, a mass of crystal, worked into the shape of an egg…