sterile anthers in, 237 Symmetry compared with heredity, 41 Symmetry of body approximate, 78 Syndactyly, 47 in foot, 48 Synthetic formulae, in nomenclature, 94 Taeniocampa, fixed and variable species, 25 Tamias, local forms of, 132 Tanagers, geographical races of, 159 Teeth, variation in, 67,39 Tephrosia consortaria and consonaria, 137,139,140 Tephrosia species, separated by season, 119 Terminal members, variation of, 68 Thais rumina, local variation in, 27 Tolerance, persistence of diversity due to, 17,134 Tomato, number of cells in fruit, 46 Transitional populations, rarity of, 165 an example, 178 Tropaeolum, sterile anthers in, 237 Trypanosomes, variation in, 215 Tusk, of Elephant, segmented, 38 of Narwhal, 44 Twinning, 41,44,71 heredity of, 45 in organs, 46 Uria troile, variety of, 150 Vanessa urticae, effects of temperature, 191 Variation, a medley of phenomena, 14,15 sporadic, 131,134 and locality, 118 Causes of genetic, 86,87,131,212 Substantive and meristic, 83 Veronica, specific difference in, 16 intermediates between species, 17 Vertebrae, division in, 60,61 homologies of, 66 Vespa, specific difference in, 23 Vortex, living organism compared with, 40 Wave-motion compared with repetition of parts, 62,67,79 Wheat, cumulative factors in, 116 climatic experiments on, 195 Woodpecker, 234 Zebra, pattern of stripes compared with ripples, 38 INDEX OF PERSONS PAGE Ackermann, 242 Agar, 218 Allen, J. A., 132,147,159 Annandale, 47 Arrigoni degli Oddi, 167