mammals just can be human eyes; for examplse photoreceptors are Rods and cones,
have single lens eyes which form an image
3 types of cone cells which detect colour (red. blue, green)... and what ever else about human eyes (function of cornea lens...)
insects have compond eyes consisting of many ommatidia made of a cornea and crystalline cone. each ommatidia forms single picture (unlike humans which 2 eye= one picture, alhtough makes them good at detecting motion). insects are able to detect colour, although less colour (like from red of visible specturum) and UV
other animal: flatworm
cupeye, photopigment ocelli
no image is formed, just able to detect light
umm that may be a help...