ORIGIN OF THE DIVERSE FORMS OF ANIMAL LIFE 84? 



From herb to towering tree, 

 From cell to creeping worm, 

 From man to what shall be ; 

 This is the lesson of all time, 

 This is the teaching of the voice sublime." 



The sequence of forms in the successive rock strata 

 makes it evident that under the stress of a rapidly changing 

 environment certain individuals of a species changed in 

 habit and structure so as to persist in the struggle among 



FIG. 388. Photograph of the fossil feet of three-toed horses iu the Museum of 

 Natural History. 



associates for food, and thus gave origin to a new variety 

 or kind of animal, while those of the species which did not 

 change to a more advantageous habit and structure be- 

 came extinct. For instance, records clearly show that the 



