The comparative study of morphology and anatomy of organisms have evolved from common ancestor.
(i) Homologous organs : The homologous organs are those which have inherited from common ancestors with similar developmental pattern in embryos. The fore limbs of mammals are homologous structures. A human hand , a front leg of a cat, flipper of a whale and a bat.s wing look dissimilar and adapted for different functions. Their mode of development and basic structure of bone are similar.
(ii) Analogous organs : The analogous organs look similar and perform similar functions but they have different origin and developmental pattern. The function of the wings of a bat, the wings of a bird and wings of an insect are similar, but their basic structures are different.
(iii) Vestigial organs : The degenerated and nonfunctional organs of animals are called vestigial organs. The same organs are found to be well developed and functional, in some of the related forms. Some of the vestigial organs in man are vermiform appendix, nictitating membrane, caudal vertebra and coccyx, etc.
(iv) Atavism : The reappearance of ancestral characters in some individuals is called atavism. e.g. Presence of rudimentary tail in new born babies, presence of thick hair on the human body.
