Explanation:
Darwin proposed the theory of evolution and also the mechanism of how the species evolved that is through natural selection.
He produced so many evidence which supported his hypothesis and one of them was that he tried to study the evolution of the eye and observed that the there are so many varieties of an eye in the different organism which is the result of the natural selection.
But his statement in his book represented in the paragraph showed that looking at the eye of organism he was puzzled and questioned himself about evolution.