Farther south, along the Florida coast, a new element comes in, that of the coral reefs, enclosing shallow channels near the shore, and thus providing sheltered harbors on their leeward side, while on their seaward side they slope steeply to the ocean. Beside this, the reef itself affords a home for a great variety of creatures, who bore their way into it and live in its recesses, as some insects live in the bark of trees. Perhaps a more favorable combination of circumstances for the development of marine life does not exist anywhere than about the coral reefs of Florida, and certainly nowhere is there a more rich and varied littoral fauna, especially on their western shore within the Gulf of Mexico. Here swims the Portuguese Man-of-War, borne gayly along on the surface of the water by its brilliant float, here the blue Velella sets its oblique sail to the wind, and hosts of the lighter and more brightly tinted corals fringe the shore with a many-colored shrubbery. In these waters are also found the blue and yellow Angel-fish, the Parrot-fish (Scarus), and the strange Porcupine-fish (Diodon). Vegetable life is comparatively scanty in these tropical waters, where there are scarcely any sea-weeds, except the corallines or limestone Algæ of the reefs. The shore of the Gulf of Mexico, as a whole, has much the same character as that of the Carolinas, until we reach the point where the mountains and plateau of Mexico come down to the coast. From this point to the Isthmus of Panama the coast is again rocky.