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sex, and condition, season of the year, or quality of the wa- 

 ter, appal by their number and confuse with their variety, 

 rendering it almost impossible to classify them. Prof. Baird, 

 of the Smithsonian Institute, writes, November 1872 : " I do 

 not think there is any one living who could do this at present, 

 especially in the absence of a series sufficiently extensive to 

 admit of the necessary comparison. I am using every effort 

 to bring together the necessary specimens in order to have 

 this work done. The published literature of the subject is 

 entirely incomplete and unsatisfactory. We have taken for 

 granted certain resemblances that did not actually exist, and 

 we must fall back upon an entirely new investigation, based 

 upon large numbers of specimens from many localities, and 

 represented by individuals of every age and sex." 



The elementary principles of comparative anatomy are so 

 simple that a child may understand them. In respect to fish 

 the species are distinguished from each other by the structure 

 of the fins, the shape of the gills, and the system of the teeth. 

 Any permanent or unvarying difference in these, coupled to 

 other varieties of color, form, habit, or the like, which might 

 seem casual, are held sufficient to constitute a distinct species. 

 The teeth of fishes indicate as clearly their habits and" mode 

 of feeding as do the teeth of quadrupeds inform the natur- 

 alist whether they are carnivorous, graminivorous, or rumi- 

 nating. In the same family of fishes the difference in the 

 dental system is often very marked ; but in the absence of 

 reliable data as to age, sex, and other conditions necessary to 

 a comparison, the naturalist may well despair of making a 

 perfect classification. 



Under the great generic divisions known as the Abdominal 

 malacopterygii, or those which have their fin-rays soft and 

 flexible, is classed the family of " Salmonidae," which are 

 characterized by an adipose second dorsal fin. " No other 

 family has it " except the Saluridce, or catfish. Of the " Sal- 

 monidse " there are endless varieties and sub-generamigra- 

 tory, non-migratory, and anadromous which include those 



