Ear

The ear is the organ of the sense of hearing, and in mammals is also an organ of balance. In mammals, the ear is usually described as having three parts—the outer ear, middle ear and the inner ear. The outer ear consists of the auricle or pinna, and the ear canal. The middle ear includes the tympanic cavity and the three ossicles. The inner ear consists of the bony labyrinth which contains the semicircular canals, and the utricle and saccule of the vestibular system, to do with balance, and the cochlea a part of the auditory system.

The ear develops from the first pharyngeal pouch and six small swellings that develop in the early embryo called otic placodes, which are derived from ectoderm.

A number of conditions may relate to the ear, including hearing loss, tinnitus and balance disorders including vertigo, however these may also relate to diseases affecting the pathways in the brain relating to hearing and balance.

Although the entire organ is considered as the ear, it is often just referred to as the visible outer part. In most mammals, the visible ear is a flap of tissue that is also called the pinna (or auricle in humans) and is the first stage in hearing. The ears of vertebrates are placed somewhat symmetrically on either side of the head, an arrangement that aids sound localization.

Animal

Animals are multicellular, eukaryotic organisms of the kingdom Animalia (also called Metazoa). All animals are motile, meaning they can move spontaneously and independently, at some point in their lives. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their lives. All animals are heterotrophs: they must ingest other organisms or their products for sustenance.

Most known animal phyla appeared in the fossil record as marine species during the Cambrian explosion, about 542 million years ago. Animals are divided into various sub-groups, some of which are: vertebrates (birds, mammals, amphibians, reptiles, fish); molluscs (clams, oysters, octopuses, squid, snails); arthropods (millipedes, centipedes, insects, spiders, scorpions, crabs, lobsters, shrimp); annelids (earthworms, leeches); sponges; and jellyfish.

Etymology

The word "animal" comes from the Latin animalis, meaning having breath, having soul or living being. In everyday non-scientific usage the word excludes humans – that is, "animal" is often used to refer only to non-human members of the kingdom Animalia; often, only closer relatives of humans such as mammals, or mammals and other vertebrates, are meant. The biological definition of the word refers to all members of the kingdom Animalia, encompassing creatures as diverse as sponges, jellyfish, insects, and humans.