The water has an assistant in its cruel inroads, and the peace of mind of the property-holders along the lower Mississippi is constantly disturbed by the presence of a burrowing pest which lives in the artificial dikes, and is always working for their destruction. This little animal is the crawfish (Astacus Mississippiensis) of the western states, and bores its way both vertically and laterally into the levees. This species of crawfish builds a habitation nearly a foot in height on the surface of the ground, to which it retreats, at times, during high water. The Mississippi crawfish is about four inches in length, and has all the appearance of a lobster; its breeding habits being also similar. The female crawfish, like the lobster, travels about with her eggs held in peculiar arm-like organs under her jointed tail where they are protected from being devoured by other animals. There they remain until hatched; but the young crawfish does not experience the metamorphosis peculiar to most decapods. These animals open permanent drains in the levees, through which the water finds its way, slowly at first, then rapidly, until it undermines the bank, when a crevasse occurs, and many square miles of arable and forest lands are submerged for weeks at a time. The extermination of these mischievous pests seems an impossibility, and they have cost the Mississippi property-owners immense sums of money since the levee system was first introduced upon the river. The city of New Orleans is built upon land about four feet below the level of the Mississippi River at high-water mark, and, running along the great bend in the river, forms a semicircle; and it is from this peculiar site it has gained the appellation of "Crescent City." The buildings stretch back to the borders of Lake Pontchartrain, which empties its waters into the Gulf of Mexico. All the drainage of the city is carried by means of canals into the lake, while the two largest of these canals are navigable for steamers of considerable size. Large cargoes are transported through these artificial waterways to the lake, and from it into the Gulf of Mexico, and so on along the southern coast to Florida. [Map from New Orleans to Mobile Bay.] CHAPTER IX. ON THE GULF OF MEXICO LEAVE NEW ORLEANS.-- THE ROUGHS AT WORK.-- DETAINED AT NEW BASIN.-- SADDLES INTRODUCES HIMSELF.-- CAMPING AT LAKE PONTCHARTRAIN.-- THE LIGHT-HOUSE OF POINT AUX HERBES.-- THE RIGOLETS.-- MARSHES AND MOSQUITOES.-- IMPORTANT USE OF THE MOSQUITO AND BLOW-FLY.-- ST. JOSEPH'S LIGHT.-- AN EXCITING PULL TO BAY ST. LOUIS.-- A LIGHT-KEEPER LOST IN THE SEA.-- BATTLE OF THE SHARKS.-- BILOXI.-- THE WATER-CRESS GARDEN.-- LITTLE JENNIE.