The material for the investigations which are described in this article was collected at Princeton, N.J., except a few specimens of Triton alpinus kindly given me by Professor H. F. Osborn. Through a failure to obtain adult specimens at the time when I obtained the embryos, there remains room for doubt as to the exact species of the embryos. The Ambly-stoma embryos correspond exactly to Clarke’s1 description of the embryos of Amblystoma punctatum, but there is one difference in the appearance of the egg-membranes which leads me to think that this may be a different species from that described by Clarke. It is, perhaps, A. bicolor, for which Jordan2 gives only the habitat New Jersey. The Frog embryos are either Rana halecina or R. palustris. I judge them to be the former. In the stages of development with which my work has dealt there are probably no specific differences in the embryos.