During evolution, some structures become nonfunctional in the organisms. These structures were otherwise working in their ancestors. These structures are called vestigial organs. Example: appendix in humans.
Homologous organs are the organs present in the organisms of different species and have the same basic structure. These species are supposed to have shared a common ancestor during their evolution. Therefore, they have organs with the same basic structures but are modified to perform different functions. For example, wings of bat and arm of humans have the same skeletal structure.
