Homonomous metamery refers to the strict repetition of an anatomical segment, known as a metamere. Although the trait is rare and seen more in the fossil record than in living organisms, homonomous metamery involves the repetition of an identical anatomical structure with the same function. Evolutionary biologists speculate that this condition was common during the early evolution of plant and animal life, but that these repeated structures evolved slightly different forms and functions as life became more complex and had to complete more-varied life processes. In this process, metamerism played a key role in the diversification of organisms, allowing animals and plants to grow in new directions as they reproduced the nervous and circulatory structures necessary to keep new body parts alive.
Heteronomous metamery is more difficult to detect in animal anatomy but still a very important trait in the functioning and evolution of animal species. Essentially, heteronomous metamery describes a situation where metameres have developed somewhat different forms or functions, but keep certain analogous elements with other metameres. Perhaps the clearest example in the animal kingdom, the segments of an insect's body -- head, thorax and abdomen -- exhibit similar structures and some shared functions, but have evolved along specialized lines that have differentiated them slightly from analogous groups of metameres.
As a very diverse animal group containing a huge number of species, frogs exhibit various anatomical structures, making it somewhat difficult to identify a common example of metamerism across the group. As vertebrates, however, all frogs have a backbone and spinal column, a good example of metamerism in itself. As in other vertebrates, the backbone is composed of a series of similar bones arranged in a line, each slightly different to provide different levels of mobility along the spinal chord, but each also similar to the next in its shape and role in the series. Each vertebrae is a metamere in a heteronomous metamery system, where each unit has a slightly different form but is clearly related to others in a repeated structure.
The circulatory system of a frog is made up of a repeated pattern of blood vessels leading to smaller capillaries that perform the same exchange processes. Even though the shapes of blood vessels and capillaries can change depending on their location in the body, they all complete a similar function, just as bronchial arches and nerve endings reproduce functions through the organism's body. This reproduction of functions allows organisms to complete similar tasks in different places and anatomical situations, ultimately simplifying the amount of genetic information an organism must carry in order to perform vital processes throughout the body.