ij^ STRUCTURE AND FORMULA OF FIN-RAYS. 



developed for their support. These bones are of two 

 kinds ; one, dagger-shaped, are plunged, so to speak, up 

 to the hilt, in the flesh between the neural spines, and 

 between the hsemal spines ; those along the upper surface 

 of the fish are called "interneural spines," in, Cut 9 ; those 

 on the under surface are the "interhsemal spines," ih. 

 The interneural spines support the " dermoneural spines, 

 dn, forming the rays of the dorsal fin or fins, Dl, D2, and 

 the upper rays of the caudal fin. The interhsemal spines 

 support the dermohsemal spines, dh, which form the rays 

 of the anal fin, A, and the lower rays of the caudal fin, 

 dh, C. 



Both dermoneural and dermohaemal spines may present 

 two structures; they may be simple, unjointed, firm, bony 

 spines; or they may be flexible, jointed, and branched 

 rays. Those fishes which have one or more of the hard 

 spines at the beginning of the pectoral, ventral, dorsal, 

 and anal fins are called " acanthopterygian," or spiny- 

 finned fishes (Grr. acanthos, spine ; ]}terux, fin) ; those in 

 which the vertical fins are supported by soft spines are 

 called "malacopterygian," or soft-finned fishes (Gr. ma- 

 lahos, soft ; and pterux). Ichthyologists avail themselves 

 of the number and kind of rays in the fins to characterize 

 the species of fishes, and adopt an abbreviated formula 

 and symbols to express these characters. 



In regard to the sea-perch (Fig. 9), the fin-formula 

 would be as follows : — 



D7,l + 12 : P12 : Vl + 5 : A3 + 8 : C18, 

 which signifies that D, the dorsal fin, has, in its first divi- 

 sion, 7 rays, all spinous ; in its second division, 1 spinous 

 -f (plus) 12 rays that are soft. P, the pectoral fin, has 

 12 rays, all soft. V, the ventral fin, has one spinous -f 5 



