Not only the Cobras, but several harmless snakes, are able to raise the anterior third of the body vertically, when taking up a threatening attitude in the presence of an enemy, at the same time widening or inflating the region behind the head. Most snakes can climb, and in this case the ribs and ventral shields are of great assistance. The Tree-snakes, usually characterized by a very slender, sometimes compressed, body, or by a prehensile tail, are specially adapted for twining themselves round branches, and in several of them the presence of a keel on each side of the ventral and subcaudal shields, accompanied by a notch corresponding to the keel, affords an additional help for climbing on vertical uneven surfaces, such as the trunks of trees. This condition of the ventral shields has a bearing on the extraordinary mode of locomotion with which some Tree-snakes (_Chrysopelea_, and probably also _Dendrophis_) have long been credited by the Malays. We allude to the so-called Flying-snakes, remarkable for their habit of shooting down from trees and descending to the ground at an oblique angle, the body being kept rigid the whole time of the "flight." It has been observed in _Chrysopelea_ that the ventral surface between the lateral keels, which may be compared to hinges, can be drawn in and become deeply concave, whilst at the same time a slight dorso-ventral flattening of the body takes place. During this muscular contraction the snake is like a piece of bamboo bisected longitudinally, and is buoyed up in such a way as to explain its parachute-like descent. All snakes are able to swim, and the more aquatic kinds may spend a few hours under the water. A _Python molurus_ is known to have remained alive in a basket sunk for thirty-six hours in a river. The best adapted for aquatic life are the Hydrophiinæ, or Sea-snakes, most of which never leave the water, and are quite helpless and soon die when brought on shore; their body is more or less compressed posteriorly, and the tail oar-shaped. Sea-weeds and barnacles sometimes settle on them. Algæ have also been observed growing on the fresh-water snake _Herpeton tentaculatum_. As regards food, Burrowing-snakes, as well as a few small Ground-snakes, subsist mostly on worms, insects, and myriopods; Tree-snakes on lizards, frogs, birds and their eggs; Water-snakes on fishes and batrachians. Among the other types, some show a predilection for mammals, others for lizards or snakes, whilst not a few feed indiscriminately upon mammals, birds, reptiles and batrachians, even on slugs, insects, and worms, in addition. However surprising, it is a fact that spiny mammals are occasionally eaten, spines of the Madagascar Hedgehog (_Ericulus_) having been found in the excrements of a _Boa madagascariensis_. Even hard-shelled eggs and molluscs may constitute the principal or exclusive food of certain snakes.