Organs with similar structure / same ancestry / anatomically same/ same origin developed along different directions due to adaptation / different needs. to perform different functions. 

For example the fore limbs of some animals (Vertebrates) like whales, bats, cheetah and human have similar anatomical structure (i.e. humerus, radius, ulna, carpals,metacarpals and phalanges) develop differently to meet different needs / to perform different functions.

Detailed Answer:

Homologous organs are the organs having fundamental similarity in structure and origin but different function. They represent a case of divergent evolution. Divergent evolution is the process by which related species become less similar in order to survive and adapt in different environmental condition. 

For example, human hand, Whale's flippers, Bat's wing, and Cheetah's foot. All these perform different function, but are constructed on the same plan. Thus, in these animals, the same structure developed along different directions due to adaptations to different needs.