THE Classification or biebs. 253 



and various attempts at improvement have from time to time 

 been made. It was considered that these groups did not respond 

 to or express those deeper affinities which were deemed to bind 

 various groups of birds together. 



The Class of Birds was by no means the only one in which the 

 existence of deep or essential affinities were thought to contra- 

 dict that system of grouping which the adoption of merely super- 

 ficial characters had brought about. Not only was it clearly 

 seen that Bats were far more really like Whales than they were 

 like Birds, but it became manifest that the close association of 

 the exclusively aquatic Dugong and Manatee with the exclusively 

 aquatic Porpoise and Dolphin was an unnatural association. 



The wide adoption of the theory of Evolution gave an easily 

 comprehensible explanation of a difference between superficial 

 resemblances and those which were deemed to be deep and 

 essential ones. The latter were thenceforth assumed to be 

 always the result of a descent from common ancestors, and 

 certain signs of genetic affinity. It seemed the easiest thing in 

 the world to discover what the different lines of inheritance 

 had been, and elaborate tables of descent — tables of phylogeny — 

 were rapidly drawn up by Haeckel of Jena and his followers. 



Naturally the great wish of Ornithologists who aspired to be- 

 come the exponents of more profound views was to discover what 

 were the lines of descent in the class of Birds. It became their 

 predominant desire so to classify Birds that their classification 

 should by itself indicate what the main lines of " descent " 

 during the process of Evolution had, as a matter of fact, been. 

 Many zealous and admirable efforts were successively made in 

 this direction. In the meantime, however, the phylogenetic 

 tables, drawn up too hastily for other classes of animals, turned 

 out one after another to be more or less unsatisfactory and 

 untenable. 



Nor can it be denied that the efforts of Ornithologists in this 

 direction have been disappointingly destitute of satisfactory and 

 certain results. It had gradually become recognized, with 

 respect to other classes of animals, that many similarities of 

 structure must have had an independent origin, and it had, and 

 has since, become increasingly difficult to discriminate and draw 

 safe and accurate lines between resemblances due to inheritance 

 and resemblances due to some other cause or causes. 



In the Class of Birds, the numbers of kinds in which is so 

 prodigious, while the differences which separate them are so 



