Eyed and Eyeless Astyanax mexicanus (image) University of Maryland Caption Except for the loss of eyes and pigment seen in the cave-dwelling form, the surface-dwelling (at top) and cave-dwelling fish (at bottom) are hard to tell apart. You can study evolution very nicely if you have both the ancestral and derived forms of evolving animals. Credit Masato Yoshizawa Usage Restrictions Credit: University of Maryland, Masato Yoshizawa. Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.