head to peel back on itself, until the snake is able to crawl out of its skin, effectively turning the moulted skin inside-out. This is similar to how one might remove a sock from one's foot by grabbing the open end and pulling it over itself. The snake's skin is often left in one piece after the moulting process, including the discarded brille (ocular scale), so that the moult is vital for maintaining the animal's quality of vision. The skins of lizards, in contrast, generally fall off in pieces. In arthropods In arthropods, such as insects, arachnids and crustaceans, moulting is the shedding of the exoskeleton (which is often called its shell), typically to let the organism grow. This process is called ecdysis. It is commonly said that ecdysis is necessary because the exoskeleton is rigid and cannot grow like skin, but this is simplistic, ignoring the fact that most Arthropoda with soft, flexible skins also undergo ecdysis. Among other things, ecdysis permits metamorphosis, the sometimes radical difference between the morphology of successive instars, and the fact that a new skin can replace structures, such as by providing new external lenses for eyes. The new exoskeleton is initially soft but hardens after the moulting of the old exoskeleton. The old exoskeleton is called an exuviae. While moulting, insects can't breathe. In dogs Most dogs moult twice each year, in the spring and autumn, depending on the breed, environment and temperature. Dogs shedding much more than usual are known as "blow coats" or "blowing coats". In amphibians Both frogs and salamanders moult regularly and consume the skin, with some species moulting in pieces and others in one piece. Gallery See also Abscission (Shedding, more general) References External links Moulting in Chicken and other fowl Animal developmental biology Skin Ethology de:Häutung