THE SCALES OF FRESHWATER FISHES. 



T. D. A. COCKERELL, 

 UNIVERSITY OF COLORADO. 



Professor N. S. Shaler, 1 writing of his experiences as a student 

 under Agassiz, said: "I acquired a considerable knowledge of 

 the literature of ichthyology, becoming especially interested in 

 the sytem of classification, then most imperfect. I tried to follow 

 Agassiz's scheme of division into the order of ctenoids and ganoids, 

 with the result that I found one of my species of side-swimmers 

 had cycloid scales on one side, and ctenoid on the other. This 

 not only shocked my sense of the value of classification in a 

 way that permitted of no full recovery of my original respect 

 for the process, but for a time shook my confidence in my master's 

 knowledge." 



I quote this, because the breakdown of Agassiz's original system 

 of classification by scales affected not only Professor Shaler, 

 but many others, to the detriment of lepidology. Dr. Jordan, 

 in his great work, "A Guide to the Study of Fishes" (1905), 

 devotes only two pages to the discussion of scales, with a couple 

 of figures. In the descriptions of fishes published by various 

 authors, much is made of the number and size of the scales, but 

 little of their structure, and it rarely happens that an ichthy- 

 ologist even takes the trouble to remove a scale from the fish 

 he is studying, in order to determine its characters. These re- 

 marks apply especially to the teleosts the ordinary fishes of 

 modern times, and it is of course true that students of the "ga- 

 noids" and their allies, mostly fossil, have never neglected the 

 scales. The ganoids have greatly thickened scales, usually 

 rhombic in form, which are well preserved in the rocks; as Agassiz 

 so well insisted, they afford a most important aid to the classi- 

 fication of these animals, particularly in the numerous cases in 

 which the skeleton is poorly preserved. Recent researches, while 

 destructive to certain theories which Agassiz considered im- 



1 Atlantic Monthly, February, 1909, p. 222. 



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