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.
Nervous tissue first arose in wormlike organisms about 550 to 600 million years ago. In vertebrate species it consists of two main parts, the central nervous system (CNS) and the peripheral nervous system (PNS).The CNS contains the brain and spinal cord. The PNS consists mainly of nerves, which are enclosed bundles of the long fibers or axons, that connect the CNS to every other part of the body.ervous tissue first arose in wormlike organisms about 550 to 600 million years ago. In vertebrate species it consists of two main parts, the central nervous system (CNS) and the peripheral nervous system (PNS).