INDEX. 



195 



Silurian, age, 90 ; life of, 94 

 Size, increase in, 144 

 Skeleton, development of, 142 

 Soft-bodied animals, 141 

 Specialization, new lines of, 183 

 Speculations on life, value of, 46 

 Spontaneous generation, n, 35 



Terrestrial life, rarity of, 160 

 Tertiary, 92, 116 



Tree-like arrangement of organ- 

 isms, 164 



Triassic age, 91 

 Tyndall, 36 



j Types, of fossil and living animals, 

 1 20 ; history of, 123 



Unicellular life, 59, 64 



! Vermes, history of, 107 

 Vertebrata, history of, no 

 Vital force, 29 ; and physical en- 

 ergy, 17 



