238 



INDEX 



Slave- making ants, 81 

 Sleeping sickness, 139 

 Slums, effect of upon inhabitants, 



154-5 



Snails in Madeira, 131 

 Sommer's repetition of Brown - Se- 



ard's experiments, 144 

 Species, attempted definition of, 75 

 breeding true not a test of, 74 

 fertility not a test of, 74 

 nature of, 74 

 Poulton on, 75 

 Ray Lankester on, 75 

 Thomson on intermediate links 



between, 76 

 Sperm, 22 

 Sperms, dimorphic, 194 



production of, 26 

 Sphex, transmission of instincts in, 



145-8 



Spindle, formation of, 14-17 

 Spireme, definition of, 14 



structure of, 14-19 

 Starch grains in peas, inheritance of, 



182-3 



Stilifer linckia; parasites upon star- 

 fish, 94 



Stylonychia, life-cycle of, 2 

 Symbiosis, Convoluta and Algte, 95 

 examples of, 95 

 lichens (Alga: and fungi), 95 

 Syphilis, inherited, 137, 218 



TADPOLES, Yung's experiments upon, 



192 

 Tarsius spectrum, adaptation against 



in pitcher-plant, 87 

 Teeth, growth of, 159-60 

 Theories of evolution, 54-8 

 Thiselton-Dyer on mutations, 72 

 Thomson, J. A., on intermediate 



links between species, 76 

 on nucleus as bearer of hereditary 



characters, 34 

 Transmission of characters, two oppo 



site modes of, 182 

 Trout hybrids, 117-8 

 Trypanosomes, 139-43 



effect of selection upon, 139-142 

 Tuberculosis, immunity to, 106, 



215-6 

 possibility of eliminating infection, 



215-6 



traces of infection generally pre- 

 sent, 107 

 Typhoid, possibility of elimination 



of, 216 

 Typhlopone (African driver-ant), 150-1 



UNFERTILISED ova, experiment* 



upon, 30 



Unicellular animals, Gruber's ex- 

 periments upon, 32 

 regeneration in, after injury, 32 

 Unicellular organisms, definition of. 2 

 fertilisation in, 2, 2 ( J 

 life-cycles of, 2, 3, 29 



VARIABILITY a character amenable 



to selection, 71 

 Variations 



in Cypris, Weismann on, 60 



in flaphnia, E. Warren on, 60 



Darwin on large and small, 62, 72 



different kinds of, 62 



difficulty in observing, 59, 61 



eliminated by bi-parental repro- 

 duction, 129, 165 



in Entomostraca, 60 



essential differences in, between 

 animals and plants, 67, 70 



fluctuating, 63 



frequency of regressive, 1 10 



in germ-cells, 164-5 



in grafts, 67-8 



inborn, see Inborn variations 



individual, see Individual variations 



large, eliminated by natural selec- 

 tion, 101 



large and small, not defined, 62 



in parthenogenetic forms, 60 



in polyzoa, Harmer on, 60 



progressive, 109 



racial, in snails in Madeira, 131 



racial, in wide-ranging species, 131 



regressive, 109 



regressive and progressive, at all 

 stages of development, 111 



said to be increased by crossing 

 races, 132 



small, the material of evolution, 129 



small, sufficiency of, 97 



theory of causation, 124 



universal, 59 



useless, elimination of, 126, 130, 

 165 



Wallace on large and small, 63 



in wild and domesticated races, 



comparison between, 70 

 Verworn on relation between nucleus 



and cytoplasm in heredity, 38 

 Village sheik, 120 



Vries, H. de, mutation hypothesis, 

 63-76 



statement of the mutation hypo- 

 thesis, 72-3 



theory of germ-plasm, 58 



