Animals are a major group of organisms, classified as the kingdom Animalia or Meta­zoa. In general they are multi­cellular, capable of locomotion, responsive to their environment, and feed by consuming other organisms. Their body plan becomes fixed as they develop, usually early on in their development as embryos, although some undergo a process of metamorphosis later on. More specifically, animals can be defined as heterotrophic eukaryotes without cell walls, which move through a blastula stage in early development. The word "animal" comes from the Latin word animal, of which animalia is the plural, and is derived from anima, meaning "vital breath" or "soul". Common usage of the term refers to so called lower animals - a brute or a beast, though can extend, contemptuously or humourously to include particular, more bestial individuals.