 The eyes of tadpoles lack lids , but at metamorphosis , the cornea becomes more dome @-@ shaped , the lens becomes flatter , and eyelids and associated glands and ducts develop . The adult eyes are an improvement on invertebrate eyes and were a first step in the development of more advanced vertebrate eyes . They allow colour vision and depth of focus . In the retinas are green rods , which are receptive to a wide range of wavelengths . 
