ORIGIN OF THE DIVERSE FORMS OF ANIMAL LIFE 345 



each of these was created direct from lifeless material seems 

 very improbable, though until 1859, when Charles Darwin 

 published his " Origin of Species," this was generally be- 

 lieved. The Bible describes briefly the creation of the 

 various groups of 

 animals on several 

 successive days. 

 These days instead 

 of being twenty- 

 four hours, as for- 

 merly understood, 

 are now considered 

 to have been long 

 periods of time, 

 each equaling sev- 

 eral million years. 

 The earth's surface 

 was once entirely 

 covered with water 

 holding in solution 

 or suspension large 

 quantities of min- 

 eral matter, which settling to the bottom from time to time 

 hardened into strata (layers) of rock. The skeletal portions 

 of the animals dying also dropped to the bottom, and oft- 

 times left the indelible impressions of their bodies in the 

 forming rock, or the skeletal structure was itself replaced 

 with stone (fossilized). By contraction of the earth's crust 

 certain portions were forced up out of the water and made 

 ready for habitation by land animals. These coming to the 

 water to drink or rushing into the lakes to escape from their 



FIG. 386. Bacteria causing consumption (tubercu- 

 losis) ; six or seven germs resembling minute rods 

 are present. Photograph magnified one thousand 

 diameters. 



