CHAPTER XII.

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