| ?Caespitum, | 127 |
| ?trochoides, | 127 |
| ?nemoralis and hortensis, | 128 |
| Helminthophila, geographical races of, | 157 |
| Hemerophila abruptaria, melanic, | 142 |
| Hepialus humuli, in Shetland, | 119 |
| Heterostyle plants, | 236 |
| Hieracium, | 9 |
| Himantopus, | 234 |
| Homoeosis, | 68 |
| Hybernia progemmaria, | 139 |
| Hybrids, sterility of, | 233 et seq. |
Incompatibility between certain allied species, | 239 |
| Individual, geometrical independence of, | 58 |
| Inhibiting Factors, | 95 |
| Intermediates, nature of, | 131, 135 |
| Isolation, consequences of, | 118 |
Lacerta muralis, Kammerer's experiments on, | 209 |
| ?fiumana, | 210 |
| Leptinotarsa, Power's experiments on, | 218 |
| Limbs, extra, in pairs, | 72 |
| Limnaea, sinistral, | 134 |
| Linaria vulgaris, self-sterility, | 239 |
| Loasa fruits, right and left, | 57 |
| Lobster, extra claws, | 76 |
| Locality, variation connected with, | 14, 118, 146 et seq., 208 |
| Lumbricus, regeneration, | 77 |
| Lychnis dioica and vespertina, inter-relations of, | 18 |
| ?macrocarpa, possibly a common parent of, | 19 |
Machetes pugnax, polymorphism of male, | 28 |
| Maize, Blaringhem's experiments on, | 229 |
| Maize, cumulative factors in, | 116 |
| Malformations, dominants, arising de novo, | 89 |
| Manx Cat, heredity, | 46 |
| Matthiola, | 84, 104, 113 |
| Melanic varieties, | 135 et seq. |
| Memory, analogy with heredity, | 190 |
| Meristic variation, | 69, 83, 86 |
| Mirabilis, striped, | 57 |
| Models of segmentation, | 59, 6 7" class="pginternal">207 |
| ?geographical variation of, | 208 |
| Segmentation, nature of, | 63 |
| ?simulated mechanically, | 64 |
| ?compared with rippling, | 65 |
| ?analogies with, | 68 |
| Segmentation of normally unsegmented structures, | 38 |
| Selection, Natural, an insufficient cause of definiteness of types, | 17, 134, 142 |
| Sempervivum, | 250 |
| Serial Homology, the true nature of, | 62, 66 |
| Setina, Alpine varieties, | 181 |
| Sex of Twins, | 44 |
| Sex-factors, possible coupling of, | 111 |
| Sexual characters, variation in, | 119 et seq. |
| Siamese twins, | 44 |
| Silky Fowl, | 84-85 |
| Simocephalus, changed by environment, | 218 |
| Sinistral forms, | 33-34 |
| Situs transversus, | 43 |
| Skate's jaws, variation in, | 38 |
| Sloths, vertebral variation, | 68 |
| Species, conceptions of, | 3, 94, 99, 240, 245 |
| ?allied, distribution of, | 185 |
| ?alternative uses of the term, | 245 |
| Specific difference, universality of, | 12 |
| ?of organisms compared with those of inorganic materials, | 15 |
| ?failure of theory of Selection to explain, | 18, 134, 247 |
| Sphyropicus varius, | 149, 156 |
| Spilosoma lubricipeda, varieties of, | 181 |
| ?Zatima, Heligoland form, | 181 |
| Spinal nerves, segmentation of, | 67 |
| Sporadic variation, | 131, 134, 248 |
| Squashes, polymorphism of, | 100 |
| Staphylococcus pyogenes, variation in, | 213 |
| Sterility of hybrids, in general, | 233 |
| ?in Lychnis hybrids, | 20 et seq. |
| ?in crossing forms of Draba, | 243 |
| ?Significance of, | 244 |
| ?Self, | 238 |
| Stilt, |
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