SIGNIFICANCE OP THESE COMPARISONS 219 



each form of animal that shows an advance over another in 

 the structure of its organs aids in locating the time of its 

 development and its relation to other forms. The group- 

 ing of animals according to their relative development of 

 structure is the basis of the classification of animals in 

 the zoology of to-day, and the view that each form of 

 animal has developed from a lower form is called the 

 Doctrine of Evolution. 



