Homologous structures are those that:

A common example of homologous structures is the forelimbs of vertebrates, where the wings of bat, the arms of primates, the front flippers of whales, and the forelegs of dogs and horses are all derived from the same ancestral tetrapod structure. Evolutionary biology explains homologous structures adapted to different purposes as the result of descent with a modification from a common ancestor ...

Answer

Homologous structures that, because of their similarity, suggest a connection with a common ancestor.