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Show 192 MR. R. I. FOCOCK ON HORN GROWTH [Mar. 21, animal, remarked tliat it " evidently bent its horns when young, probably in a fence." This explanation, however, even if no other were forthcoming, would not, in my opinion, account for all the peculiarities of the case. For, apart from the more deep-seated modifications enumerated below, the horns differ in three particulars from those of a typical Prongbuck-namely, in direction, in the practical suppression of the anterior tine, and in shape, being subcylindrical and lacking the lateral compression and basal antero-posterior width observable in the normal horn. An injury of the nature suggested might perhaps produce permanent malformation ; but it seems hardly likely that with subsequent growth the malformation would follow the same line of development in the two horns, and result in identity in length and similarity in shape and symmetry. After the appearance of the notice in the ‘ Field,' Mr. Thomson, the Assistant Superintendent of the Gardens, discovered that the Prongbuck had been castrated. Castration usually has a marked effect upon secondary sexual characters ; and since the discrepancy in size between the horns of the bucks and does of Antilocapra justifies the inclusion of these structures in that category of organs, one would expect abnormality in the growth of the horns to be caused by the operation in question. I am not aware that any observations on the effects of castration on the Prongbuck have yet been published. In the case, however, of Fallow Deer, its results have been recorded in a few cases by Dr. G. H. Fowler (P. Z. S. 1894, pp. 485- 494), who summarises his results, based upon the evidence of undisputed data, under five headings, as follows :-(1) Complete castration at birth may result in the formation of simple dags. (2) Castration late in life may produce great asymmetry in the antlers. (3) Antlers of castrated deer can be shed ; if castrated after the horns for the year are burnished \i. e. have lost the velvet], the animal may shed them prematurely; antlers put up after castration may be retained for at least two years. (4) Partial castration soon after birth may result in a comparatively feeble but normal development of the antlers. (5) Castration on one side may result in the nearly normal development of one antler, and in abnormality and reduction of the other*. Although the shedding of the antlers in Deer is a phenomenon only analogous to that which takes place in the Prongbuck, and although the horns of the Prongbuck, inasmuch as they are sometimes, at all events, present in the female, have not quite so strong a claim to be regarded purely as secondary sexual organs as those of the Fallow Deer, where they are confined to the male, we should nevertheless look for somewhat similar variations to be caused by castration in the two animals. And assuming the * A valuable summary o f this question may be found in Mr. J. T. Cunningham's book on ‘ Sexual Dimorphism in the Animal Kingdom ' (1900). I learn from Mr. F. C. Selous that castration does not appreciably affect the horns o f the Eland. In that Antelope horns occur in both sexes. |
