Naegeli, C., 26 Natural selection, 11, 140, 142, 149 Nettleship, E., 175 Night-blindness, 175 _Pararge egeria_, 132 Parkinson, J., 122 Pea comb, 33 Peas, coloured flowers in, 24 Peas, tall and dwarf, 18 Pigeons, 86 Pin-eye in primulas, 55 _Pisum_, 17 Primulas, 31, 55, 68, 93 Pollen, 3 Pollen of sweet peas, 92 Pomace fly, 115 Population, inheritance of characters in a, 147 Presence and Absence theory, 35 Pure lines, 162 Purity of gametes, 24 Purity of type, 155 Rabbits, 53, 60 Ratios, Mendelian-- 3 : 1, 20 9 : 3 : 3 : 1, 25, 34 9 : 3 : 4, 51 9 : 7, 49 Ray, John, 143 Recessive characters, 19 Repulsion between factors, 90 Reversion, 59, 165 in rabbits, 59 in sweet peas, 62 in fowls, 65 in pigeons, 65 Rose comb, 33 Saunders, E. R., 54, 122 Seeds, nature of, 4 Segregation, 22 Selection, 162 Sheep, horns in, 76 Silky fowls, 30, 105 Single comb, 32 Species, nature of, 150 Species, origin of, 11 Speckled wood butterfly, 132 Spermatozoa, 3 Sports, 147 Staples-Browne, R., 66 Sterility, 151 Sterility in sweet peas, 93 Stocks, double, 122 Stocks, hoariness in, 54 Sweet pea, colour in, 44, 79 history of, 82 inheritance of hood in, 89 inheritance of size in, 62 Telegony, 167 Thrum-eye in primulas, 55 Toe, extra toe in poultry, 76 Tschermak, E., 29 Unit-character, definition of, 31 Variation, 14, 137, 139 Walnut comb, 33 Weismann, A., 13 Wheat, beard in, 74 experiments with, 157 White, dominant in poultry, 72 Wilson, J., 168 Yellow mice, 119 Zygotes, nature of, 5 * * * * * Notes * * * * * [1] Cf. note on p. 171. [2] It has been found convenient to denote the various generations resulting from a cross by the signs F_1, F_2, F_3, etc. F_1 on this system denotes the first filial generation, F_2 the second filial generation produced by two parents belonging to the F_1 generation, and so on. [3] Hurst's original cross was between a Belgian hare and an albina Angora, which turned out to be a masked Dutch. [4] The Spot is an almost white bird, the colour being confined to the tail and the characteristic spot on the head. [5] The reader who searches florists' catalogues for these varieties will probably experience disappointment. The sweet pea has been much "improved" in the past few years, and it is unlikely that the modern seedsman would list such unfashionable forms. [6] It is to be understood that wherever a given factor is present the plant may be homozygous or heterozygous for it without alteration in its colour. [7] It should be mentioned that as the shape of the pollen coat, like that of the seed coat, is a maternal character, all the grains of any given plant are either long or else round. The two kinds do not occur together on the same plant.