Metamerism is a phenomenon in which the body of organisms is constructed into a linear series of body segments. Organs and tissues in the body of such organisms are found to be repeated after regular intervals (segments) and each segment is known as a metamere or somite. Metameric segmentation is characteristic of Annelida and Arthropoda. In an earthworm, the body consists of 100-120 ring-like segments or somites called metameres. It shows true segmentation corresponds with internal segmentation. Cockroach also shows the metameric segmentation. Its anterior few segments are specialized to form the head. Such metamerism is called heteronomous metamerism.