One of the most interesting of these ten-footed crustaceans is the blind crayfish of Mammoth Cave. It is found also in various subterranean streams of the country. The eyestalk of these little creatures is all that remains to tell the story of what was once an eye, and they live and thrive in perfect darkness. The ordinary crayfish of Western streams has a peculiar habit of burrowing, which at times has occasioned great damage in undermining dikes and dams. I once came upon a remarkable crayfish community in Indiana. There had been a flood the day previous, and every log in the neighborhood and the piers of the bridge were covered with crayfish which, in this locality at least, appeared to be endeavoring to escape from too much water. On all sides, some yards from the creek and high above it, the ground was raised into small heaps six or eight inches across, each, as I discovered, being the home of a crayfish, and as far as the eye could see on the prairie were these mounds and heaps, suggestive of the vast numbers of these little animals in this vicinity. XVI. THE CRABS Of all the crustaceans, the crabs are the most singular and certainly the most intelligent. Rapid in movement, good swimmers, alert, garbed in extraordinary colors, often in stolen homes, they attract attention at once and are the harlequins and clowns of the animal kingdom. The crabs are distinguished from the rest of the group principally by their very short tails. Their bodies are round, elongated, or oval. They are found almost everywhere, from the deep sea, where they occupy shells and sometimes drag about a luminous sea anemone, to every beach. It is in or near the tropics that the most remarkable crabs are seen. During a visit to the islands off the coast of Texas, I once found a remarkable crab community. The islands were flat sand banks just above the surface, blown and washed up by the sea, with here and there sand dunes and shrubs, and again vast stretches of sand inhabited only by crabs. The latter were all of one kind, a pale gray, so mimicking the sand in color that it was almost impossible to distinguish one from the other. There were legions of them, the sand in places being fairly riddled with their burrows, into which they darted with inconceivable rapidity. As I walked along the sands they ran ahead in rapidly increasing numbers, then divided and were so quick of foot that it was impossible to run them down. This vast army of crabs was the sanitary corps of the island, devouring every dead fish that came ashore and other animal matter of all kinds. [Illustration: FIG. 147.--A land crab (_Gecarcinus_).]