THE CLASSIFICATION OF BIRDS. 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 utile 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 

