368 Classification of Fishes 



series variously and divergently branched, with each group at 

 its earlier or lower end passing insensibly into the main or primi- 

 tive stock. A very little alteration now and then in some 

 structure is epoch-making, and paves the way through speciali- 

 zation to a new class or order. But each class or order through 

 its lowest types is interlocked with some earlier and otherwise 

 diverging group. 



Defects in Taxonomy. A sound system of taxonomy of 

 fishes should be an exact record of the history of their evolu- 

 tion. But in the limitations of book-making, this transcript 

 must be made on a flat page, in linear series, while for centuries 

 and perhaps forever whole chapters must be left vacant and 

 others dotted everywhere with marks of doubt. For science 

 demands that positive assertion should not go where certainty 

 cannot follow. A perfect taxonomy of fishes would be only 

 possible through the study, by some Artedi, Miiller, Cuvier, 

 Agassiz, Traquair, Gill, or Woodward, of all the structures of 

 all the fishes which have ever lived. There are many fishes 

 living in the sea which are not yet known to any naturalist, 

 many others are known from one or two specimens, but not yet 

 accessible to students in other continents. Many are known 

 externally from specimens in bottles or drawings in books, but 

 have not been studied thoroughly by any one, and the vast 

 multitude of species have perished in Palaeozoic, Mesozoic, and 

 Tertiary seas without leaving a tooth or bone or fin behind 

 them. With all this goes human infallibility, the marring of 

 our records, such as they are, by carelessness, prejudice, depend- 

 ence, and error. Chief among these defects are the constant 

 mistaking of analogy for homology, and the inability of men 

 to trust their own eyes as against the opinion of the greater 

 men who have had to form their opinions before all evidence 

 was in. Because of these defects, the current system of classifi- 

 cation is always changing with each accession of knowledge. 



The result is, again to quote from Dr. Coues, "that the 

 natural classification, like the elixir of life or the philosopher's 

 stone, is a goal far distant." 



Analogy and Homology. Analogy, says Dr. Coues, "is the 

 apparent resemblance between things really unlike as the wing 

 of a bird and the wing of a butterfly, as the lungs of a bird and 



