A very curious adaptation of means to ends in the modification of the virus is its swiftly fatal effect on birds. A stricken child, though half crazed with fear, may run a distance of three miles before paralysis begins to impede its motions; a squirrel will escape to its nest in the top of the tree, only to come forth again and topple down in its delirium; but a bird drops as if he had swallowed a dose of prussic acid. Serpent virus is specifically a bird poison; in other words, it acts instantaneously in cases where a few moments' delay would defeat the purpose of the snap bite. Wounded rodents will not run very far and can be relied upon to come out of their holes; but a bitten bird, unless promptly paralyzed, would fly out of sight and drop in distant thickets, beyond the ken of its destroyer. And of all bird-killing reptiles the fer-de-lance is the most destructive. The Spaniards have varied its bill of fare by importing the wherewithal of an occasional rabbit stew, but during the preceding ages it had to subsist on poultry, like a popular circuit preacher--the _hutia_ rat having developed a talent for avoiding its haunts. The alleged _horror naturalis_ of serpents is perhaps not more deep-rooted than the aversion to cats; at all events, the West Indians have overcome it sufficiently to prefer rat-killing snakes to tabbies. In thousands of rancho cabins a pet serpent of the genus _coluber_ may be seen gliding noiselessly along the rafters, or slip through the crack of a floor plank to reach the penetralia of the basement, where the death shriek of rodents soon after announces the result of its activity. Aristocratic Creoles relegate it to their stables, but the tenants of numerous backwood _casuchas_ furnish it a cotton-stuffed bed box, and reward its services with a weekly dish of milk. There are several species of large river serpents, and one true boa, the Cuban _matapollos_, or chicken-killer, that attains a length of eighteen feet, and has been known to use its supernumerary coils for the purpose of cracking the ribs of a hound flying to the assistance of the barnyard rooster. In addition to the above-mentioned jungle tortoise there are several land turtles of the genus _chlemmys_, and thousands of chelidonians are annually caught on Samana Bay, southern Porto Rico, St. Vincent, the Isle of Pines, and the north coast of Matanzas, Cuba. Those of Santiago Bay have gradually been exterminated, but a large number of West Indian fishing waters are practically inexhaustible. A specialist like Agassiz might haul nondescripts from scores of Haytian coast rivers, and the angle fishers of the Cuban sierra brooks can hook an equally interesting reproduction of an Appalachian species.