The evolution of man: a popular exposition of the principal points of human ontogeny and phylogene . the fin is alreadyessentially modified, in that the rays on one side of the stemare partly or altogether lost, and are retained only on theother side (Fig. 268). Hence arises the half-feathered, oruniserial fish-fin, inherited by the other fishes from theSelachii (Fig. 269). Gegenbaur first showed how the five-fingered leg ofAmphibia is developed from this uniserial fin (Fig. 270) andis inherited by three classes of Amniota. In those Dip-neusta which were the ancestors of the Amphibia, the fin
The evolution of man: a popular exposition of the principal points of human ontogeny and phylogene . the fin is alreadyessentially modified, in that the rays on one side of the stemare partly or altogether lost, and are retained only on theother side (Fig. 268). Hence arises the half-feathered, oruniserial fish-fin, inherited by the other fishes from theSelachii (Fig. 269). Gegenbaur first showed how the five-fingered leg ofAmphibia is developed from this uniserial fin (Fig. 270) andis inherited by three classes of Amniota. In those Dip-neusta which were the ancestors of the Amphibia, the fin rayson the other side of the stem also were gradually degradedin development, and were in a great measure lost (the light-coloured cartilages in Fig. 269). Only the four lowest rays(shaded in Fig. 269) were retained; and these are the fourouter digits of the foot (second to fifth digits). The first,or great digit (toe), on the contrary, originated from thelower part of the fin-rod. From the middle and upper partsof this fin-rod developed the long main stem of the limbs 302 THE EVOLUTION OF Fig. 267. Fig. 269.
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Keywords: ., bookcentury1800, booksubjectembryologyhu, booksubjecthumanbeings
