84 THE FOOD OF ANIMALS 



attracted a Ceratodus, and this proved that the Australian lung- 

 fish is by no means a vegetarian, as has hitherto been thought. 

 On opening the animal, the intestinal canal will indeed almost 

 always be found filled with green vegetable matter, partly com- 

 posed of leaves and blossoms of gum- and tea-trees, carried into 

 the river by the wind, partly of genuine water-plants. But noting 

 that Ceratodus took so well to animal bait, I grew doubtful 

 whether the above-mentioned plants are eaten for their own sake, 

 or for the sake of the many little animals : craw-fish, worms, snails, 

 shell-fish, and insect-larv^, which they harbour. On examining 

 the contents of the intestines, I found that the tough fibres of 

 the plants are not digested, but leave the body in an almost 

 unchanged state. They are, so to say, but the vehicles of the 

 food itself, which is of essentially animal character." 



ORDINARY BONY FISHES (Teleostei) 



The ordinary Bony Fishes (Teleostei), which include the 

 vast majority of existing piscine forms, present many examples 

 of special adaptations to an animal diet. A very large number 

 of species are provided with numerous small, pointed teeth, which 

 are of no use for masticatory purposes, but constitute an efficient 

 seizing apparatus, fatal to many sorts of prey, from other fishes 

 downwards. Among common predaceous species which possess 

 numerous teeth of this kind are the Fresh-water Perch {Perca 

 fiuviatilis) and its many allies, the members of the Mackerel 

 Family, and the voracious Pike {Esox lucius). It is the rule for 

 the teeth to be backwardly-directed, so that the prey cannot escape 

 after having been once secured. 



Lures. — A further specialization in the direction just indicated 

 is found in the ugly Angler- Fish or Fishing- Frog {Lophius 

 piscatorius) (fig. 366), common in shallow water round our coasts. 

 Here the huge mouth is beset with large, pointed teeth of various 

 sizes, those in front being hinged on the jaws so that they are 

 easily pressed down to admit of the entry of prey, for which, 

 however, exit is quite another matter, as, after depression, the 

 teeth spring up again by the action of elastic ligaments. This 

 ungainly fish lurks on the bottom, with which it harmonizes in 

 colour, the hue being capable of alteration to suit different sur- 

 roundings (aggressive variable coloration). Its paired fins are 



