The great and multiform army of the sea worms is indeed the most prolific source of markings on sea-formed rocks. Sometimes they cover very large surfaces of these, or penetrate the beds as perforations, with tortuous furrows, or holes perfectly simple, or marked with little striæ made by bristles or minute feet, sometimes with a fringe of little footmarks a each side, sometimes with transverse furrows indicating the joints of the animal's body. Multitudes of these markings have been described and named either as plants or as worm-tracks. Again, these creatures execute subterranean burrows, sometimes vertical, sometimes tortuous. These are often mere cylindrical holes afterwards filled with sand, but sometimes they have been lined with a membranous tube, or with the rejectamenta of the food of the animals, or with little fragments of organic matter cemented together. Sometimes they open on the surface as simple apertures, but again they may be surrounded with heaps of castings, sometimes spiral in form, or with dumps of sand produced in their excavation, and which may assume various forms, according to circumstances. Sometimes the aperture is double, so that they seem to be in pairs. Sometimes, for the convenience of the animal, the aperture is widened into the form of a funnel, and sometimes the creature, by extending its body and drawing it in, surrounds its burrow with a series of radiating tracks simulating the form of a starfish or sea anemone, or of the diverging branches of a plant. Creatures of higher grade, provided with jointed limbs, naturally make their actions known in more complicated ways. Some years ago I had the pleasure of spending a few weeks at the favourite sea-side resort of Orchard Beach on the New England coast, and there made my first acquaintance with that very ancient and curious creature the Limulus, or Horse-shoe Crab, or King-crab, as it is sometimes called. Orchard Beach is, I presume, near its northern range on our coast, and the specimens seen were not very large in size, though by no means rare, and not infrequently cast on shore in storms. But the best facilities for studying their habits were found in a marsh at no great distance from the hotel, where there were numerous channels, ditches and little ponds filled with sea water at high tide. In these were multitudes of young Limuli, varying from an inch to three or four inches in breadth, and though many were dead or merely cast shells, it was easy to take young specimens with a landing net. A number of these were secured, and I made it my business for some time to study their habits and mode of life, and especially the tracks which they made in sand or mud.