INTRODUCTION 



The observations in this book have been made at intervals during twenty-five 

 years. Less clearly realized at first, more clearly later, always the guiding prin- 

 ciple has been that light on the process of evolution should be obtainable from 

 study of its product, that in the very texture of the color pattern of animals, in 

 the complex web of relations binding species to species, the play of cause and 

 effect by which they were made should be decipherable. 



So much ground has been covered in the course of the inquiry that it does not 

 seem wise to attempt to present all the results in one volume. 1 Hence the hidden 

 interest to which reference has been made seems even more obscure than it 

 might otherwise have been. Its existence, however, and minor changes in front 

 in serving it, explain an unevenness in the work, which before anyone else the 

 ichthyologist will appreciate. 



There are so many kinds of fishes, and they do so many things in different 

 ways, at different times and places, that it has proved quite impossible to find 

 out all of interest about any one, or how all of them do a particular thing. But no 

 reasonable effort has been spared to discover the truth with the same degree of 

 accuracy for all. 



The faunas and floras of every region include names of species of doubtful or 

 no validity. Each of the latter, of course, represents some misconception of fact. 

 These misconceptions arise from different causes, often quite beyond the power 

 of the taxonomist to control. But these species falsely conceived, when accepted 

 at face value, tend to blur the conception we have of species as groups existing in 

 fact. Unless some correction is applied on their account, they tend to invalidate 

 inferences drawn from the statistics of taxonomy. 



I have endeavored to bring a field naturalist's experience to the aid of taxon- 

 omy. It has proved necessary to refer many species to synonymy. The decision in 

 every instance has been based, not on the ground that the nominal species so 

 treated does not differ enough from some other to justify recognition under a 

 distinct name, but on the ground that it does not differ at all. For the most part 

 the changes introduced are based upon nothing more than recognition of un- 

 suspected sexual dimorphism, or of the effects of age, transient color change, the 

 accidents of imperfect preservation, and the like. They rectify previous judg- 

 ments in a large enough number of instances to give some suggestion regarding 

 the type of error the taxonomist is most likely to commit, and the genera and 

 species whose relationships he is most likely to misconceive. 



In a few points comparisons of the record will show that my observations re- 

 peat those of Jordan and Thompson (Bull. U. S. Bur. Fish., vol. 24, 1904 (1905), 



1 That Dr. Longley intended to write other treatises on his studies at Tortugas is brought 

 out here. The other work or works would have dealt with his "hidden interest" (see next 

 sentence in text), namely, the bearing his observations had on the process of evolution. The 

 bibliography presented herewith contains subjects of papers dealing wholly or in part with 

 evolution. — S. F. H. 



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