Question

why is that the eye of the octopus and mammals come under analogous structure when its basic structure is same? If brains of fish and mammals can come under homologous structures because of its basic structure then why not the eye?

Answer 1

Although the octopus and man are very different life forms, between which no so called evolutionary relationship can exist, their eyes have exactly the same structure! This is a clear sign that similar structures do not constitute proof of evolution.
Confronted by this situation, evolutionists say that these organs are not homologous (that is, descended from a common ancestor) but rather analogous-similar, despite the absence of any evolutionary relationship.In their view, for instance, the human eye and the octopus eye are analogous organs.