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Show 220 DR. H. GADOW ON THE EVOLUTION [Mar. 18, renewal of the hairy coat is likewise repeated by the horny sheath. This stage is still represented by Antilocapra, although the horny sheath by continued basal growth gradually envelops also the greater part of the pedicle. (Text-fig. 25, III, p. 216.) IV. Direct continuation of types II and III, still repeated stage by stage ontogenetically. An improvement towards the preponderance of the intercrinal horn-substance, the conversion of the sheath into a morphologically well-finished horn-sheath, the suppression of the hairs, and of periodical shedding of any part of the whole compound weapon, was only a question of time with onward evolution, This, the highest and most perfect stage, is represented by the typical Antelopine or Bovine Ruminants, of which their peculiar member, the Prongbuck, still falls short. They are morphologically the highest, palseontologically the latest of Ruminants. Herewith it agrees that horns are carried by both sexes, whilst the inheritance of these organs by the females is still a rare exception amongst the Cervince. Moreover, these weapons, having become permanent and evergrowing, and therefore useful throughout the year, are of much greater value to their bearers. (Text-fig. 25, IV, p. 216.) Attention has already been drawn in this paper to the important fact that the horns of a young calf still contain a considerable number of hairs mixed up in the sheath, and that in older animals such hairs are restricted to the more basal portions; secondly, that the top cone of the hornshoe is shed. In Ewes this first generation falls off as a thin, transparent cap of the size and shape of half a hazel-nut. In fact this first cap of the Bovine horn is in every respect homologous with the shedding sheath of the Prongbuck. The Oxen, Sheep, and Goats now exhibit only once a process of shedding which in their immediate ancestors must have been of frequent occurrence, and which in the Prongbuck is still a periodical feature. The types I, II, III, and IV, exemplified by the Eocene Dinoceras, the Cervinos since the Lower Miocene, the Prongbuck, still existing, and the hollow-horned Ruminants or Bovince, are an illustration of onward phyletic evolution; and these stages are still faithfully repeated in the development of the recent species. Ontogeny is a shortened recapitulation of phylogeny. Titles of the more important Literature referred to in the text. SANDIFORT, G. Over de Vorming en Ontwikkeling der Horens van zogende dieren in het algemeen en van die der Herten-beesten in het bijzonder. Nieuwe Verhandl. i. Klasse Tvoningl. Nederl. Inst. Wetenschap. ii. (1829). pp. 67-106; with 7 plates. |
