1. The peculiar ticking which causes the coat pattern known as “steel” in Dutch rabbits may be represented as a heterozygous character. 2. The factor for this character, calledX, may be considered as a darkening or melanising factor, similar toD in the “agouti-blacks” of Punnett, but rather weaker in its effect. In a heterozygous condition, it converts an agouti rabbit into a steel; and in a homozygous condition, it converts an agouti into a black. 3. The data show that blacks extracted from steels, and therefore homozygous forX, when mated to agoutis (homozygous forx) give nothing but steel; and moreover, the same blacks when mated to normal blacks or chocolates (aaxx) give nothing but steel. 4. There is some evidence to show that there may be more than one type of agouti, for two agouti males were used, which when mated to steels gave equal numbers of steel and agouti, but when mated to extracted blacks, one gave nothing but steel, the other both steel and agouti. On this point, further investigations are being made.