THE DERMAL FIN-RAYS OF FISHES. 467 



Indeed, are there any characters against which the same 

 objections may not be urged ? 



Paradoxical as it may seem, yet the most superficial 

 structures are often of the deepest significance in the stndy 

 of phylogeny. As a mammal may be snrely identified by its 

 liair, and a bird by its feather, so may a fish be classified by 

 its dermal fiu-ra3^ The dermal rays, however, are of even 

 more constant structure than the body-scales. There seem 

 to be only three main types of these rays, and it was with 

 the object of defining these types, and of traciug out tlieir 

 phylogenetic relations, that this work was nndertaken, in the 

 hope of thereby helping to clear up some obscure points in 

 classification. Unfortunately the task has proved far less 

 easy than I expected, chiefly on account of the many diffi- 

 culties enconntered in the study of fossil forms. The work 

 remains incomplete; many important questions are left 

 nndecided ; yet I hope enough has been done to show that it 

 is a fruitful field for research, from which much may be 

 expected. 



The bulk of this work was carried out on the material in 

 the Department of Comparative Anatomy of the Oxford 

 Museum. I have to thank Professor Sollas for the loan of 

 specimens from the Geological Department, and Professor 

 Zit tol for permission to freely examine the famous Mnnich 

 collections. More especially I am indebted to Dr. R. H. 

 Traqnair and Dr. A. Smith Woodward for much help and 

 advice whilst working through the collections in the Edin- 

 burgh and British Museums. 



The dermal rays of fish have already been described in 

 considerable detail by many authors. In the first half of the 

 nineteenth century Agassiz, in his classical memoir (1), 

 mentioned the bony and geuerally jointed rays of the higher 

 fish, and the unjointed horny rays of the Selachians and 

 Chim£era. He also described the slender horny rays in the 

 embryonic fins of Teleostean fish, and the dermal rays of 

 many fossil forms. Bruch in 1861 (5) first drew a clear 

 distinction between the endo-skeletal rays and the secondary 



