THE DERMAL FIN-RAYS OF FISHES. 491 



specialised in sti-ucture^ the dermal rays may have preserved 

 many primitive characters which the scales have lost. Into 

 the question of the exact homology of the Teleostean scale 

 itself I do not propose to enter; we may well adopt the 

 generally accepted view that they were derived originally 

 from the bony basal plate of the " placoid " scale. It should 

 also be borne in mind that it might be urged that the thin 

 scales of modern Teleosts may possibly represent a second 

 generation of dermal organs^ substituted for and developed 

 outside the older scales. The familiar fact that the scales in 

 these fish may overlie the dermal bones of the skull and 

 opercular apparatus^ and may cover the lepidotrichia them- 

 selves (as in Chsetodoutidfe^ see page 477); seems to support 

 this theory. For my own part, however, I am inclined to 

 believe that such an interpretation is both unjustified and 

 unnecessary, and that the overgrowth mentioned above is 

 merely due to the late and secondary extension of the scaling 

 of the body. Even in the sturgeon itself we can see small 

 bony plates occasionally overlying the bases of the dermal 

 rays. 



Hitherto I have omitted to mention the "fulcral" scales 

 found at the edge of the fins of AcipenseridaB and Lcpidosteus. 

 In Acipenser these fulcra consist of V-shaped scales situated 

 along the dorsal surface of the caudal lobe. They obviously 

 belong to the same category of dermal skeletal organs as the 

 scales, and probably represent a right and a left scale fused 

 together. In Lepidosteus fulcral scales occur along the 

 anterior edge of the dorsal, anal, and paired fins, and along 

 both the dorsal and the ventral edge of the caudal fin. But 

 in this fish the fulcral scales are in double rows, not fused 

 together. Now whilst the fulcra pass insensibly into the 

 body-scales, as was long ago pointed out by Agassiz (1), and 

 are undoubtedly modified scales, their resemblance to the 

 neighbouring lepidotrichia points to the same conclusion with 

 regard to the latter. As Burckhardt remarks, " Fulci-a, 

 Flossenstrahlen und Schuppen sind zweifellos vcrwandto 

 Hartgebilde '^ (6). 



