Aluminium versus aluminum. Following up a Topical Words piece on the international spelling of what British English writes as sulphur, many American subscribers wrote in to ask about another element with two spellings: aluminium.
The simplest and presumably most primitive form of nervous system is termed a nerve net. In a nerve net, neurons are dispersed in a thin layer, not clustered into nerves or a central nervous system (CNS), and they are positioned seemingly at random relative to each other.he simplest and presumably most primitive form of nervous system is termed a nerve net. In a nerve net, neurons are dispersed in a thin layer, not clustered into nerves or a central nervous system (CNS), and they are positioned seemingly at random relative to each other.
Although the invertebrate nervous system is usually much simpler than the nervous systems found in vertebrates, there is still a broad range in complexity depending on the type of invertebrate. The simplest type of nervous system is found in hydras and jellyfish (cnidarians) and is referred to as a nerve net..Nerve nets do not have distinct central or peripheral regions, and lack anything that resembles a brain. Instead, the scattered nerve cells form loose networks in each cell layer of the body wall.lthough the invertebrate nervous system is usually much simpler than the nervous systems found in vertebrates, there is still a broad range in complexity depending on the type of invertebrate. The simplest type of nervous system is found in hydras and jellyfish (cnidarians) and is referred to as a nerve net..