 The radiation destroyed the DNA within the sperm, but nearly normal embryos were still produced.Gunther Hertwig repeated this experiment in 1924, using crosses between different frogs.A cross between a toad, "Amietophrynus regularis", and a frog, "Rana fusca", would not produce a viable embryo, but fertilization of a toad egg by an irradiated frog sperm would produce a haploid larva.