Tissue is a system of cells and non-cellular formations that are united by a number of common properties — structure, function, and patterns of development. Fabric, being a part of organs, provides common manifestations of vital activity, which underlie more complex functions performed by organs and their systems. Tissues originated in multicellular animals in the process of evolution. Based on the primary relationship with the environment associated with food intake, two primary tissues were formed - epithelial tissue (see), separating the body from the external environment, ensuring its protection and external metabolism, and connective tissue (see), which is the morphological basis of internal reactions exchange. The increasing complexity of the animal's relationship with the environment, the need to ensure irritability and mobility led to the gradual development of nervous and muscular tissue. Neural tissue (see) has the ability to perceive irritation, as well as produce and transmit nervous excitement. Muscle tissue (see) provides the mobility of individual parts of the body and its mobility as a whole. In accordance with its functions, each fabric has a specific structure.