DEVELOPMENTAL MODIFICATIONS IN THE SAND DOLLAR CAUSED BY COBALTOUS CHLORIDE IN COMBINATION WITH SODIUM SELENITE AND ZINC CHLORIDE

¹ Dept. of Biological Sciences, Northwestern University, Evanston, Illinois, and The Hopkins Marine Station, Pacific Grove, California

1. Newly fertilized eggs of D. excentricus were allowed to develop in single and combined sea water solutions of cobaltous chloride, sodium selenite, and zinc chloride.

2. Combination solutions of cobalt and selenite were additive in causing the development of radial larvae and almost additive in causing polar elongation of the larvae.

3. In solutions of equivalent strength the development of exogastrulae was highest in cobalt, next in the combination, and least in the selenite solutions.

4. Solutions of zinc caused effects that were similar to those of cobalt but in concentrations that were 1/100th the latter.

5. Combination solutions of cobalt and zinc gave effects that indicated synergistic action.

6. It is suggested that the effects of cobalt, selenite, and zinc are through their reaction with the thiol groups of certain enzymes and that the greater effect of zinc is because of a greater affinity for such groupings.