CHAPTER XI 
CLASSIFICATION OF FISHES 
well ice * is a natural emaaae a “the mind which 
Ww}) always strives to make orderly disposition of its 
knowledge and so to discover the reciprocal relations and 
interdependencies of the things it knows. Classification pre- 
supposes that there do exist such relations, according to 
which we may arrange objects in the manner which facilitates 
their comprehension, by bringing together what is like and 
separating what is unlike, and that such relations are the 
result of fixed inevitable law. It is therefore taxonomy (raézs, 
away; vopos, law) or the rational, lawful disposition of observed 
facts.” 
A perfect taxonomy is one which would perfectly express 
all the facts in the evolution and development of the various 
forms. It would recognize all the evidence from the three ances- 
tral documents, paleontology, morphology, and ontogeny. It 
would consider structure and form independently of adaptive 
or physiological or environmental modifications. It would 
regard as most important those characters which had existed 
longest unchanged in the history of the species or type. It 
would regard as of first rank those characters which appear first 
in the history of the embryo. It would regard as of minor 
importance those which had arisen recently in response to 
natural selection or the forced alteration through pressure of 
environment, while fundamental alterations as they appear one 
after another in geologic time would make the basal characters 
of corresponding groups in taxonomy. In a perfect taxonomy 
or natural system of classification animals would not be divided 
into groups nor ranged in linear series. We should imagine 
* Key to North American Birds. ° 
157 
