A 



THE 



POPULAR SCIENCE 



MONTHLY. 



MAT, 1903. 



THE CLASSIFICATION OF FISHES. 



By President DAVID STARR JORDAN, 



LELAND STANFORD JR. UNIVERSITY. 



/CLASSIFICATION, as Dr. Elliott Coues has well said, is a natural 

 ^-^ function of "the mind which always strives to make orderly dis- 

 position of its knowledge and so to discover the reciprocal relations 

 and interdependences of the things it knows. Classification presup- 

 poses 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 laws. It is, there- 

 fore, Taxonomy (rd^i^, array; pofio^^ law) or the rational, lawful dis- 

 position 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 be 

 based on morphology, the consideration of structure and form inde- 

 pendent of adaptive, or physiological, or environmental modifications. 

 It would regard those characters as most important which had existed 

 longest unchanged in the history of the species or type, thus consider- 

 ing all knowledge derived from paleontology. It would regard as of 

 minor importance those traits which had risen recently in response to 

 natural selection or to the forced alteration through pressure of environ- 

 ment, while fundamental alterations as they appear one after another 

 in geologic time would make the basal characters of corresponding 

 groups in taxonomy. In greater or less degree, the life history of the 

 individual, through the operation of the law of heredity, repeats the 

 actual history of the group to which the individual belongs. For this 

 reason the characters appearing first in the individual are likely to 

 have greatest importance in classification. 



