When Cod Become Blind

Severa! largo cod are kept in one oí the tanks of tbo Arasterdam aquarium, uscessarily near the surface, and therefore exposed to a strong light from above. Now, the cod, though not a deep sea flsi:. ia not a snrface swirnmer aud live ,it depths where the sunlight must b? very mueh modified by passage through the water. It lives iu wbat to us would be semidarknesa. Every one of these cod exposed to the strong light is suffcring from an extraordinary hypertrophy of the eye. The "ole organ has beeome overgrown, as if in the effort to adjust itseJf to the use of more light rays it had become overequipped and then useless. The cod in fact, are bliud. The most interesting feature in this change is the extraordinary rapidity with which increased supply of light rays has overdeveloped the organ for its use. It has taken place, not by slow j degrees from individual to individual, but in a course of time to be measured by months and in every individual in the tank. If this exatnple is a measure of the rapidity with which such changes take place among fish, the adaptation of those creatures which have migrated from the shallow waters of the deep seas, shown by the total loss o,r enormous development of their eyes and the growth of illuminating organs to light the abyss, may have been as rapid as it is marvelous.