If the brain has evolved to reverse the image formed at the back of the retina so that we see the right way up, this must mean that there were animals whose vision was upside down. Is this true? Are there any animals who still see in this way?
No...your coming at the premise slightly wrong....as the eye developed in the first animals the brain was developing to cope with this new sensory input as well...the first eyes were only good for seeing extreme contrasts and large motions....but as the brain was growing at the same time the "correction" that you talk about developed along with the eyes improvement so I am not aware of any animals that see this way.....there may be some out there though....As an interesting aside you can actually buy glassses which will re-invert your vision for you and if you wear them continuously for a number of days the brain will adapt and cope with this till your new upside down world becomes the right way up again....though once you take them off it again take a number of days to re-adapt to the normal state of affairs.