tHE DERMAL FIN-RAYS OF FISHES. 495 



bone-cells of the lepiuotricliia are seen to be of just tlio same 

 type as those of the scale, if somewhat smaller. 



Protospoudyli. — The extinct fisli allied to Amia give 

 evidence of having- had quite the same history. On passing 

 from the more modern to the earlier and more primitive 

 types, such as the Semionotida3, Macrosemiidas, and Eug- 

 nathidge, Ave recognise the appearance of ganoine on the 

 surface of the lepidotrichia, and of f ulcral scales at the edge 

 of the fins. There is also an increasing correspondence 

 between the body-scale and the ray in histological structure. 



-i^theospondyli. — The same story is told by the remains 

 of these fish, with this difference, — that even the living 

 Lepidosteus has lost neither the ganoine nor the fulcra 

 (p. 477). 



Chondrostei. — We now come to a group of fish whose 

 dermal rays are of a distinctly more primitive character than 

 are those of the foi'egoing sub-orders of the Actinopterygii. 

 In all the known Isospondyli, Protospondyli, and ^Etheo- 

 spondyli, the lepidotrichia correspond in number with, and 

 are articulated to, the endo-skeletal supports in the dorsal 

 and anal fins. Moreover these rays scarcely penetrate below 

 the body-scales, except where a secondary overgrowth of the 

 scale-bearing skin has taken place. In the Chondrostei, on 

 the contrary, the dermal rays are always more numerous than 

 the endo-skeletal supports, and are not specially related to the 

 latter, but form an evenly distributed layer over the fin (see 

 p. 479). The proximal segment of the lepidotrichia extends 

 some little way beneath the body-scales, so as to embrace 

 and overlap the extremity of the endo-skeletal ray. 



In the degenerating series which leads from the Cliondro- 

 steidse to the Acipenseridge (A. S. Woodward [42]), we 

 can trace the same tendency to lose the ganoine and the 

 f ulcral scales so constantly met with in those groups of 

 fish which have survived to the present day. But in the 

 other families of the Chondrostei these characters are gener- 

 ally well preserved. The Palseouiscidce are by far the most 

 instructive family to study for our present purpose. The 



