THE EVOLUTION OF ANTS 



between similar species of wild organisms, for the process 

 of racial development or evolution is so exceedingly slow that 

 even some slight structural changes may have required mil- 

 lions of years, or at any rate periods far too long to fall 

 under the observation of a being so ephemeral as man. The 

 proofs of this very long historical evolutionary process are 

 therefore indirect; they derive their value from the con- 

 vergent and mutually corroborative inferences drawn from 

 studies made in widely different fields of the great science 

 of biology. At least five of these fields furnish significant 

 historical inferences — the study of fossil animals and plants 

 (palaeontology) , the comparative study of the development 

 and structure of existing forms (morphology, or anatomy and 

 embryology), the study of the present geographical distri- 

 bution of plants and animals (chorology), the study of the 

 classication of plants and animals (taxonomy), and the com- 

 parative study of the behavior of animals (ethology). Obvi- 

 ously, the study of extinct or fossil species is of the greatest 

 value, but the record of some species is deplorably frag- 

 mentary and most of the specimens found are imperfectly 

 preserved. Although, therefore, all positive palaeontological 

 data are precious, the fact that we have not yet found con- 

 necting or intermediate forms at particular geological hori- 

 2ons may be of slight significance. Comparative morphol- 

 ogy and its shorthand expression, classification, are of 

 enormous value in determining the possible genetic relation- 

 ships between species, both living and fossil, and the distri- 

 bution of living species as compared with that of their fossil 

 allies is of great historical significance. Finally, the study 

 of the behavior of existing animals and of the dependence 

 of behavior on the structure and function of particular organs 

 enables us to draw inferences in regard to the actual modes 

 of life of their allied extinct species. After these very general 



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