INDEX 



201 



feeding of, 87, 88 



nervous organization, 86 



receptors, 89 



sense organs, 90 



structure, 86 



tentacle, effect of detaching, 87 

 Secretions, interstitial, effect on ner- 

 vous system, 98 

 Segments, 44 

 Segregation, 170 

 Selection, 130, 143 



a negative process, 143 



ordinary, improvement by, 148 



essential processes of, 143 

 Selenka, Madame, 13 

 Self-direction, 146 

 Self-maintenance, 137 

 Senescence, 70-72 



theories of, 71 



Senile degeneration, see Senescence 

 Sensation, 82 

 Sensations, primitive, 101 

 Sense organs, retrogressive changes in, 

 73 



sea-anemone, 90 

 Sense perception, 116 

 Sensorium commune, 81 

 Sex and nervous system, 94-99 

 Sex, cause of, 62 



center of society, 98 



conditions, indifferent, 53 



definition of, 95 



determination before birth, 62 



glands, see Gonads 



reversal of, by gonad transplanta- 

 tion, 96 



transformation of, 96 

 Sextuplets, 62 



Sexual characteristics, determined by 

 gonad, 97 



primary, 96 



secondary, 96, 97 



secondary, controlled by gonad, 97 



Shere Khan, 109 

 Skeleton, cartilage, 55 



development, 55 



membrane, 55 

 Skin, development, 56 

 Skull, Calaveras, 9 



cap, Pithecanthropus, 13, 14 



Gibraltar, 23 



pre-Neandertal, 18 

 Slavery, an adjustment, 128 

 Smith, Elliot, 20 

 "Social theory," 151 

 Societal, adjustment, 136 



code, 139 



evolution, past processes, 149 



fitness, 135 



range, forces at work, 150 



realm, 149 



selection, in relation to war, 144 



selection, various forms taken by, 



145 



Societies, struggle of, 143 

 Society, and organisms, analogy be- 

 tween, 129 



human, changes in, 163 



relation of to sex, 98 



stratification of, 170 



systems, cultural adjustments, 134 

 Sollas, W. J.> 12, 34 

 Specialization, and progress, 160 



relation to regeneration, 65 

 Spencer, H. f 129 

 Sperm cells, 95 



in fertilization, 42 



structure, 42 

 Spider, instincts of, 108 

 Sponges, 90-92 



lack of nervous tissue, 92 

 Spy, Belgium, 23 

 Steinach, 71, 97, 98 



gonad transplantation, 96 

 Stimulation, effect of, in sea-anemones, 

 87 



