2. They all perform different functions in their respective animals. Since their functions are different, there is difference in their structures.
3. There are similarities in the bones of these different organs and their joints. This similarity is attributed to having developed from a common ancestor.
4. Some organisms have organs similar in function but different in structures. Such organs are termed as analogous organs. Eg. : (a) Tail fin of lobster and flukes of whale. (b) Wings of fly and wings of a bird. (c) Eyes of arthropods and vertebrates.
5. Some organisms have organs similar in structure but different in functions. Such organs are called homologous organs. Eg. : (a) The forelimbs of man (adapted for handling), bat and bird (adapted for flying), whale and seal (adapted for swimming) have the same skeletal composition. (b) The scales of an ovulate pin cone correspond with the carpels of a flower and the scales of the staminate cone correspond with the stamens of a flower.
6. Similarities observed between the homologous organs are due to the fact that evolution leads to modify the existing structures for new modified functions creating a new structure.