INDEX OF SUBJECTS 



255 



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 tempera- 

 ture 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 repeti- 

 tion of parts 62, 67, 79 



Wheat, cumulative factors in 116 



climatic experiments on 195 



Woodpecker 234 



Zebra., pattern of stripes compared 



with ripples 38 



