232 



The Mechanistic Conception of Life 



Selection, of intensity of light by ani- 

 mals, 52flf. ; natural, 50 fif. 



Sex determination, 16. 



Shearer, 11. 



Sipunculides, 141. 



Snyder, CD., 39, 208. 



Solution, protective, 172. 



Spallanzani, 113. 



Spermatozoa, 113 ff. 



Spermatozoon, twofold action of, in 

 fertilization, 12 ff., 132 ff., 161 fl. 



"Speziflsche Bildungsstoffe," 104. 



Spontaneous raovements, 71. 



Spyrogyra, 177 fif., 188. 



Standfuss, 211. 



Stereotropism, 91 ff., 223. 



Stevens, 17. 



Stieghtz, 43. 



Stockard, 206, 207. 



Strongylocentrotus franciscanus, 140, 

 198. 



Strongylocentrotus purpuratus, 8, 139 ff., 

 144, 162, 189, 197, 201, 205. 



Sumner, 80. 



Symmetry, chemical, 38, 39. 



Temperature as a cytolytic agent, 



135ff., 138ff. 

 Tower. 90, 227. 

 Traube. 96. 

 Tropisms, 26, 36 ff., 54, 55, 60, 62, 



69, 70, 72. 

 Tubularia mesemhryanthemum, 95, 97. 

 Tunicates, 92. 

 Twin formation, 19, 205. 

 Twins, production of, from egg, 204 ff. 

 Twofold action of spermatozoon in 



fertilization, 12 ff., 132 ff., 161 ff. 



Tyrosin, 23. 



Uexkuell. 70. 



" Unterschiedsempfindlichkeit," 54. 



Van Duyne, 92. 



van't Hoff, 208. 



Vanessa antiope, 220. 



Vanessa levana, 211. 



Vanessa prorsa, 211. 



Varying photosensitiveness in animals, 



45. 

 Varying susceptibility of eggs of 



different species to parthenogenetic 



development, 144. 

 Vaucheria, 188. 

 Virchow, 127, 128. 

 Vision, 79 ff. 

 Voit, 4. 

 Volvox, 51, 223. 



Waller, A. D., 222. 



Warburg, 13, 157, 160, 189. 190. 



Wasteneys, 13, 157, 181, 182. 



Water, distilled, poisonous action of 



distilled water on, 170 ff.; role of, 



in segmentation, 99. 

 Weismann, 91, 210, 211. 

 Wiener, 215. 

 "Will," 35 ff., 40. 

 Wilson, 17, 18, 19. 



X-chromosomes, 18 ff. 



"Zielstrebigkeit," 24. 

 Zimtz, 4. 



