INDEX 



167 



Stentor, regeneration in, 10 n, 47, 

 147, 149 



Stomach, in young nemertiues, 74, 

 75 



Stylonychia, reproduction in, 41 f, 

 42 



Suez Canal, 5 



Suicide, 137 



Surface-tension, 59 ;. effects of, 

 53, 86 ; alteration of, by living 

 matter, 55, 86 



Surface-volume ratio, 50, 55, 88 



Swallow, 133 



Sycon, 94 n, 147 



Symbiosis, definition, 122; exam- 

 ples of, 122, 124 



Syncytia, 137 



Tadpole, change into frog, 72, 75- 



78 



Tapeworm, 127 

 Teeth, in old age, 18 

 Teleology, errors of, 85 

 Teleost fish, 150 

 Termites, 12 

 Tools, part of man's individuality, 



14, 29 ; inorganic organs, 13 

 Trees, in old age, 18; duration of 



life, 26 

 Trypanosomes, 127 



Twins (identical), 68, 70 ; normal 

 production of, 68, 70; artificial 

 production of, 69, 70 



Volvocidae, evolution of, 102-107, 



111 

 Volvox, 95, 104, 110, 114, 138, 



150, 151, 157 



Walt Whitman, 114 



Warfare, evolution of, 115 



Water, its " metamorphosis," 76 



Weismann, on sex, 45 



Wheeler, 142 



"White ants," 5 



Whitman, 149 



Woodruff, and lack of sexual 



process in Ciliates, 71 

 Wordsworth, 141 

 Worms, Nernertine, 72-75, 79 

 Wren, size of, 86 



Yolk-sac of unhatched chick, 77 

 Yucca-plant, dependence on an 

 insect, 128, 135, 142, 158 



Zarathustra, his independence of 



accidents, 1, 3, 8 

 Zoothamnium, 100 

 Zygote, definition, 45 ; fertilized 



ovum, 67 



CAMBRIDGE: PRINTED BY JOHN CLAY, M.A. AT THE UNIVERSITY PRESS. 



