(1) By means of an operative technic it is possible to remove the egg membrane from the egg of Fundulus heteroclitus and to compare experimentally the action of salts on the egg, the embryo freed from the membrane and the newly hatched larva. (2) The effects of normal solutions of K, Na, and Ca chlorides upon the above are reported. (3) The embryo, freed from the egg membrane, is quite resistant to NaCl solutions while the hatched larva is quickly killed in the same solution. (4) The resistance of the eggs to NaCl increases with age. (5) K and Ca chlorides kill the dissected-out embryo much more quickly than the egg, while the recently hatched larva is much more sensitive to the two salts than is the embryo. (6) Combinations of these salts show antagonistic action. Na + Ca mixtures are not toxic for eggs but are markedly so for the embryo freed from the egg membrane and for the newly hatched larva.