It is well known that these horn sheaths are at times shed and reproduced, but the exact regularity with which the process takes place is by no means certain, although such direct evidence as there is goes to prove that it occurs annually in the autumn. Prong-bucks have shed on eight occasions in the Zoological Gardens at Philadelphia, five times by the same animal, which reached the gardens in October, 1899, and has shed each year early in November, the last time on October 22, 1903,[1] and the writer has seen one fine head killed about November 5 in a wild state, on which the horn-sheaths were loose and ready to drop off. [Footnote 1: It is interesting to note that the first pair shed measured 7-1/4 inches, on the anterior curve; the second pair 9-1/2, and the last three 11 inches each. The largest horns ever measured by the writer were those of a buck killed late in November, 1892, near Marathon, Texas, and were 15-3/4 inches in vertical height and 21 along the curve.] But few of these delicate animals have lived long enough in captivity to permit study of the same individual through a course of years, and the scarcity of observations made upon them in a wild state is remarkable. That irregularity in the process would not be without analogy, is shown by the case of the Indian sambur deer, of which there is evidence from such authority as that king of sportsmen, Sir Samuel Baker, and others, that the shedding does not always occur at the same season, nor is it always annual in the same buck; and by Pore David's deer, which has been known to shed twice in one year. When resemblances such as those of the prong-horn are so promiscuously distributed, the task of fixing their values in estimating affinities is not a light one, and in fact the most rational conclusion which we may draw from them is that they point back to a distant and generalized ancestor, who possessed them all, but that in the distribution of his physical estate, so to speak, these heirlooms have not come down alike to all descendants. There is again a complicating possibility that some may be no more than adaptive or analogous characters, similarly produced under like conditions of life, but quite independent of a common origin, and it is seldom that we know enough of the history of development of any species to conclude with certainty whether or not this has been the case. At all events, the prong-buck is quite alone in the world at present, and we know no fossils which unmistakably point to it, although it has been supposed that some of the later Miocene species of _Cosoryx_--small deer-like animals with non-deciduous horns, probably covered with hair, and molars of somewhat bovine type--may have been ancestral to it, but this is little more than a speculation. What is certain is that _Antilocapra_ is now a completely isolated form, fully entitled to rank as a family all by itself.