ADAPTATIONS OF FISHES. Spines of the Catfishes.--Venomous Spines.--The Lancet of the Surgeon-fish.--Spines of the Sting-ray.--Protection through Poisonous Flesh of Fishes.--Electric Fishes.--Photophores or Luminous Organs.--Photophores in the Iniomous Fishes.--Photophores of Porichthys.--Globefishes.--Remoras.--Sucking-disks of Clingfishes.--Lampreys and Hogfishes.--The Swordfishes.--The Paddle-fishes.--The Sawfishes.--Peculiarities of Jaws and Teeth.--The Angler-fishes.--Relation of Number of Vertebræ to Temperature, and the Struggle for Existence.--Number of Vertebræ: Soft-rayed Fishes; Spiny-rayed Fishes; Fresh-water Fishes; Pelagic Fishes.--Variations in Fin-rays.--Relation of Numbers to Conditions of Life.--Degeneration of Structures.--Conditions of Evolution among Fishes. 179 CHAPTER XIII. COLORS OF FISHES. Pigmentation.--Protective Coloration.--Protective Markings.--Sexual Coloration.--Nuptial Coloration.--Coral-reef Fishes.--Recognition Marks.--Intensity of Coloration.--Fading of Pigments in Spirits.--Variation in Pattern. 226 CHAPTER XIV. GEOGRAPHICAL DISTRIBUTION OF FISHES. Zoogeography.--General Laws of Distribution.--Species Absent through Barriers.--Species Absent through Failure to Maintain Foothold.--Species Changed through Natural Selection.--Extinction of Species.--Barriers Checking Movements of Marine Species.--Temperature the Central Fact in Distribution.--Agency of Ocean Currents.--Centers of Distribution.--Distribution of Marine Fishes.--Pelagic Fishes.--Bassalian Fishes.--Littoral Fishes.--Distribution of Littoral Fishes by Coast Lines.--Minor Faunal Areas.--Equatorial Fishes most Specialized.--Realms of Distribution of Fresh-water Fishes.--Northern Zone.--Equatorial Zone.--Southern Zone.--Origin of the New Zealand Fauna. 237 CHAPTER XV. ISTHMUS BARRIERS SEPARATING FISH FAUNAS.