FINS 7i 



structural adaptation associated with it, probably arose from 

 the habit found in many fishes of accompanying larger creatures 

 either for protection or gain, and of concealing themselves under 

 the shelter of any large object in the sea. "It is evident," writes 

 Dr. Regan, "that the Sucker-fishes must have been derived 

 from fishes which had, as the Pilot-fish has to-day, the habit of 

 associating with Sharks. The spinous dorsal fin of the Pilot- 

 fish {Naucrates) and of other oceanic fishes of the same type, 

 with the spines folded back within a groove, might possibly 

 have some power of adhesion if the edges of the groove were 

 applied to another object and the spines were then slightly 

 raised." 



Another remarkable modification is found in the Angler- 

 fishes or Pediculates (Pediculati) , in which the first ray of the 

 spinous dorsal fin is placed on the snout and transformed into a 

 line and bait. In the Common Angler or Fishing-frog [Lophius) 

 of our own shores, for example, this ray is quite flexible and 

 bears a membranous flag-like appendage at its tip, its function 

 being to attract the attention of small fishes when waved about 

 in the water in front of the Angler's formidable jaws (Fig. 89). 

 In the related Frog-fish [Antennarius) and Bat-fish {0 gcocephalus) 

 (Fig. 40D) the line and bait is much reduced in size, and is 

 sometimes represented merely by a short tentacle lodged in a 

 cavity above the mouth. Among the Ceratioids, oceanic 

 Angler-fishes spending their lives in a region of more or less 

 perpetual darkness, the bait generally takes the form of a bulb 

 of varying size which can be made luminous at will, and acts 

 as a lamp to attract other fishes to destruction (Fig. 31). In one 

 species {Lasiognathus saccostoma) the basal part of the dorsal 

 fin-ray has been converted into a stout rod, followed by a 

 slender line, which is provided, not only with the usual 

 luminous bulb, but also with a series of curved horny hooks 

 — a complete angler indeed (Fig. 31G)! 



The anal fin, placed on the lower edge of the body between 

 the tail and the vent, may be briefly dismissed. Like the dorsal 

 it exhibits some variation both in size and form in diflferent 

 fishes. In the Gymnotids, Eels, and other forms in which it 

 functions as a locomotor organ, the anal fin is very long (Figs. 

 5f; iob); in other fishes, where it acts mainly as a balancing 

 keel, it is considerably shorter (Fig. 28); in the Ribbon-fishes 

 {Trachypterus, Regalecus) it is absent altogether (Fig. 8d). It 

 may be supported entirely by soft rays, or the first few rays may 

 be converted into stiff spines, often of some size (Fig. 28e, g). 



