Wright, W. von, on the protective plumage of the Ptarmigan.
Writing.
Wyman, Prof., on the prolongation of the coccyx in the human embryo; on the condition of the great toe in the human embryo; on the occurrence of the supra-condyloid foramen in the humerus of man; on variation in the skulls of the natives of the Sandwich Islands; on the hatching of the eggs in the mouths and branchial cavities of male fishes.
Xenarchus, on the Cicadae.
Xenophon, selection in mankind advocated by.
Xenorhynchus, sexual difference in the colour of the eyes in.
Xiphophorus Hellerii, peculiar anal fin of the male.
Xylocopa, difference of the sexes in.
Yarrel, W., on the habits of the Cyprinidae; on Raia clavata; on the characters of the male salmon during the breeding season; on the characters of the rays; on the gemmeous dragonet; on colours of salmon; on the spawning of the salmon; on the incubation of the Lophobranchii; on rivalry in song-birds; on the trachea of the swan; on the moulting of the Anatidae; on the young of the waders.
Yellow fever, immunity of negroes and mulattoes from.