The Domestic Ass and Mule.

There are two closely related animals, the domestic ass and the mule, which ought to show this inguinal pattern if affinity and variation could be fairly invoked to account for it on the theory of selection. These are also animals whose mode of life is locomotive, but in a much less degree than the horse and their paces are quieter and less free in character. What then is found in them as to the size or persistence of this pattern? In the ass it is absent or nearly so (I have found one example of its presence), and in the mule it is variable and never occupies more than half the area of that in the horse. These facts agree closely with the hybrid character of the mule and the differing activities of the horse, mule and ass. The pattern in Przewalski’s horse is small and oval and resembles that of the mule. The onager (equus asinus), which is very much like these three domestic animals in form, has an inguinal pattern, much less in size indeed than that of the horse, but well-defined, and this fact is in keeping with its character for remarkable fleetness of foot and activity. The three zebras, Mountain, Grevy’s and Burchell’s, show no inguinal pattern, in spite of their power of rapid locomo­tion and resemblance in size and form to the horse. Though they have that power they exercise it in their wild lives for their own sakes alone, in the intermittent way which is bound up with their habit of life, and not for the sake of man, as in the case of the horse.

The pectoral and inguinal regions of the domestic horse are two of the most valuable fields in the mammalian body for studying the formation by muscular action of patterns of hair, for this animal is the locomotive animal par excellence. Here the process has been carried to the extreme limit, and these two are prominent examples among the characters to which I drew attention in a paper published in the Proceedings of the Zoological Society of London, “On proposed additions to the accepted systematic characters of certain Mammals,” June 9th, 1904, Vol. I. I am still of the opinion that they deserve “Flag rank,” though they have not yet been promoted. Be that as it may I think it may be well here to compare two animals belonging to the family Equidæ, the horse and zebra, which resemble one another very closely in form—in respect of these patterns.