DORSAL FINS. 



27 



these are either 

 isolated, as in 

 Dactylopterus, or 

 united to the dor- 

 sal fin, as in most 

 fishes. The ge- 

 neral character, 

 however, of simple 

 rays is that of 

 being strong, ri- 

 gid, and so sharp 

 as to become spi- 

 nous : that these 

 spines are used as 

 instruments of de- 

 fence, becomes evi- 

 dent from the fact of many fishes suddenly raising them 

 when captured, so as to inflict wounds on the hand 

 of an incautious person ; and that they also are essential 

 to the perfect use and efficiency of the fin itself, by 

 strengthening and supporting the other rays, is also to 

 be inferred from this fact, — that in all soft-rayed fishes 

 the first ray of the dorsal, if not simple, as in the 

 carps, &c, is almost invariably stronger than the others, 

 — a structure intended to break the resistance of the 

 water during the swimming of the fish, on the very 

 same principle that a boat or vessel is furnished with 

 a stem. Fishes which swim but little, and in calm 

 waters, like the eels and a few others, do not possess 

 this peculiarity ; but in those which belong to the 

 most perfect division of the osseous fishes (the order 

 Acanthopteryges), the development of the spiny rays is 

 at its maximum, and constitute the primary distinction, 

 even by the confession of Cuvier, of this most natural 

 group. Sometimes these spines are detached and iso- 

 lated, when they are always short, and repose in a 

 groove on the back (as in Naucrates, &c.) ,• in which 

 case, however efficacious they may be for defence, they 

 can be of no use in swimming. When these spines 



