THE BLINDNESS OF THE CAVE FAUNA AND THE ARTIFICIAL PRODUCTION OF BLIND FISH EMBRYOS BY HETEROGENEOUS HYBRIDIZATION AND BY LOW TEMPERATURES

Abstract

1. It is shown that blind embryos or more correctly embryos with degenerated eyes can be produced by heterogeneous hybridization in fish embryos (e. g., Fundulus heteroclitus ♀ and Menidia ♂). Since in these cases as a rule no circulation exists the inference is possible that the anomalous condition of the eye may be due to lack of circulation. 2. Blind embryos of the pure breed of Fundulus heteroclitus may be produced by the addition of KCN to the sea water. 3. It is shown that immediately after fertilization (by sperm of their own species) and during the early stages of segmentation the egg of Fundulus heteroclitus is rapidly killed or injured if it is exposed to a constant temperature of about 0° (or slightly above); while it may be exposed to a slightly higher temperature (e. g., 7° C.) for weeks without being injured. If the egg is exposed to the low temperature after the embryo is once formed it can resist the low temperature of from 0 to 2° C. for weeks without permanent injurious effects. 4. If eggs of Fundulus heteroclitus are fertilized with the sperm of the same species and exposed immediately after fertilization for a number of hours or a day to a temperature of between 0 and 2° C. abnormal embryos can be produced a certain percentage of which may show degenerated eyes. 5. Lack of light does not influence the development of the eyes of Fundulus. 6. It is pointed out that internal mutational changes and not lack of light may account for the blindness of certain cave fish and salamanders.