IT has been demonstrated many times, in those forms whose eggs are fertilized outside the body cavity of the female, that deviations from the normal oxygen supply are capable of producing metabolic changes in the developing embryo. Since such changes result in visible disturbances of the growth of certain organs, one is led to believe that their effect might be more fundamental than the observed external anomalies, and that the germ plasm might also be influenced. This experiment was undertaken with the dual idea of attempting, by this method, to alter the developnmental rate of mammalian embryos directly, and to discover if, at the same time, a more fundamental metabolic change were produced which might affect the germ cells. The experimental procedure is given, and the behavior of the stock recorded. It should be stated at the outset that no cause and effect relationship is claimed between the experimental procedure and the results obtained. These results are given in order that other investigators may know of their occurrence. The experimental method is explained with the idea of adding another possible approach to the problem of experimental modification of the germ plasm. The experimental production of abnormalities in those forms whose eggs are either laid or developed outside the body of the female has been a fertile field of investigation. Stockard (1921) reviewed the work which had been done up to that time from the viewpoint of developmental rate and structural expression. His theory to account for the abnormalities is based on the 427