(c) : The organs which have the same fundamental structure but are different in functions are called homologous organs. These organs follow the same basic plan of organisation during their development. But in the adult condition, these organs are modified to perform different functions as an adaptation to different environments. The fore­limbs of cat, lizard, whale and bat have the same basic structural plan. In each case the fore­limb consists of humerus, radio­ulna, carpals, metacarpals and digits. The skeletal parts of the fore­limbs of all these vertebrates are similar in structure and arrangement. But the fore­limbs of these animals have different shapes and functions. In lizard they are used for walking, in cat for running, in whale for swimming and in bat for flying.