I trust you will allow me to point out that the drift of my letter on the above subject in Nature, vol. 1. p. 572, has not been fully apprehended. Hitherto we seem to have no very clear cases in which we can actually trace the operation of "natural selection." I think, when examined, this will be found to be an instance.

    The spots appear to have arisen in the dog as comparatively recent permanent markings--for protective purposes--after semi-domestication. As Mr. Worthington G. Smith says, they are not seen among wild animals allied to the dog.

    They appear to have arisen since the original Red Dog--be he Dhole, Pariah, or Dingo--became pied, and at times black, through domestication. It is only on a black coat that the tan-spots would be conspicuous, and simulate eyes.

    Perhaps Mr. A. R. Wallace may throw light on the matter. The spots seem to be the only really permanent marking among dogs, and are now being bred out.

S. E. Peal.
Sibsagar, Asam, February 19.

    Mr. Peal's suggestion appears to be a probable one, and is supported by Mr. Worthington Smith's observations (Nature, vol. 1i. p. 57). The spots may have been protective to the animals during sleep, causing them to look as if awake. The reason that they do not occur in wild dogs may be that the latter conceal themselves when sleeping, which the half-domesticated animals were not able to do.

Alfred R. Wallace.