[2] There is one other bird, not given in the above list, that is pure Sebright except that his legs are yellow. Until I find out by further breeding of the Sebright stock whether yellow legs are present in it, this case must remain doubtful. On the basis of a two factor color-difference one Sebright (as to color) is expected in 16 birds, and one in 64 on a three factor basis. Some Sebrights had been raised along with the back cross, hence the possibility of contamination. [3] Provided that the blue classification was based on the adult plumage and not on down color. [4] If the recessive mutation occurs first in the Z chromosome of an egg of the female it will not appear in the next generation; then if it has passed into a male, half his daughters will show it. The single factor-pair involved is carried by the sex chromosomes ZZ. [5] One may be either sex-linked or sex-limited so far as the evidence goes. [6] No mention is made by Baur that a heterozygous male instead of a pure silver male was used, although the male is made heterozygous in the formulæ. [7] For activity and pugnacity in hummingbirds, see Tropical Nature, pp. 130, 213. [8] The Naturalist in La Plata, W. H. Hudson, London, 1892, pp. 269-270. [9] Proceedings of the Zoological Society of London, 1885, p. 431, Quelques remarques sur le dimorphisme sexuel. Jean Stolzmann. [10] George W. and Elizabeth G. Peckham. Observations on Sexual Selection in Spiders of the Family Attidæ. Nat. Hist. Soc. of Wisconsin, Vol. I, 1889, pp, 46, 47. [11] _Loddigesia mirabilis_ has the tail about three times as long as the body. Similar modifications are found in the genera _Sappho_, _Cynanthus_, _Lesbia_, _Stegnura_, _Discura_, _Gouldia_, _et al._ [12] Among the most remarkable of this wonderful family are the nine species of coquettes (_Lophornis_), which have elongated feathers, with metallic tips, springing from the sides of the neck; some have also beautiful crests. (George W. and Elizabeth G. Peckham, Additional Observations on Sexual Selection in Spiders of the Family Attidæ, Nat. Hist. Soc. of Wisconsin, 1889, vol. I, pp. 141, 142.) [13] Tropical Nature, p. 210. The italics are ours. [14] A. H. Sturtevant, Experiments on Sex Recognition and the Problem of Sexual Selection in _Drosophila_. Journ. Animal Behavior, Sept.-Oct. 1915, vol. 5, No. 5, pp. 352, 353. [15] In the eland as well as in the reindeer, in which both sexes have horns that begin in the latter at least to develop before the gonads ripen, it is stated that castration does not prevent the development of the horns in the male, but whether they are as large as in the normal male is apparently not definitely stated. [16] Yarrell also states that after the fallow buck has reached the height of its maturity and has 6 prongs in its antler, removal of one testis causes the next antler to have but 5 prongs.