The Transfer of Coelomic Eggs between Frogs.

IN the analysis of events immediately preceding and following fertilization of the frog egg, it is frequently desirable to treat the eggs with various reagents. Any such treatment must circumvent the barrier represented by the fertilization membrane and the jelly layers. These membranes can be removed from fertilized eggs mechanically or by treatment with proteolytic enzymes (Spiegel, 1951) without impairing development. However, unfertilized eggs from which the jelly has been removed mechanically cannot be fertilized by sperm unless the jelly is restored, and chemical removal of the jelly also inhibits their ability to be parthenogenically activated (Barch & Shaver, 1959). Therefore an alternative method for obtaining jelly-free eggs for treatment prior to fertilization is necessary. Coelomic eggs are invested by a vitelline membrane, but they are free of jelly layers and the fertilization membrane has not yet been formed. This recommends them as the stage for exposure to reagents whose effects on fertilization are to be analyzed. However, although Subtelny & Bradt (1960) review circumstances under which coelomic eggs may be activated parthenogenically and develop normally, normal development is not obtained after insemination with sperm (Rugh, 1962). Apparently, normal fertilization of many eggs can only be obtained after eggs have passed through the oviduct. It therefore seemed important to determine whether or not normal fertilization could be obtained using coelomic eggs removed from a female, treated with various reagents, then returned to a host female where they could pass through the oviduct prior to insemination. Arnold & Shaver (1962), Humphries (1956) and Subtelny & Bradt (1960) obtained coelomic eggs by ligation or removal of the oviducts of donor animals prior to pituitary stimulation. Arnold & Shaver (1962), Humphries (1956) and Rugh (1962) transferred such eggs into host females through an incision made in the body cavity of anesthetized animals. Rugh (1962) reported that eggs transplanted to sexually inactive females will pass through the oviducts and collect jelly. In this case, all uterine eggs are of donor origin. However, jelly secretion is not normal and the percentage of eggs fertilized is low. Normal results are only obtained if sexually active hosts are used. To identify the donor