Comparative anatomy is the study of organs in different species with the aim of establishing whether the organism are related.Organisms which have the same basic features are thought to have arisen from a common ancestor.
The vertebrate pentadactyl limb evolved in different ways as an adaptation to different modes of life.e.g. as a flipper in whales, as a wing in bats and as a digging hand in moles.
Such organs are said to be homologous, i.e. they have arisen from a common ancestor but they have assumed different functions.This is an example of divergent evolution .
The wing of a butterfly and that of a bird are said to be analogous.i.e. they have originated from different ancestors but they perform the same function.This is an example of convergent evolution.
All organisms share some form of common ancestor, however, butterflies are categorized as insects, whereas bats are categorized as flying mammals. There is no scientific proof or fossil records indicating that either species is closely related, therefore, wings have evolved independently in these two species. Thus the wings of both species can be considered an analogous trait.