138 A HISTORY OF FISHES 



of Izaak Walton. "By a leather-mouth," he writes, "I mean 

 such as have their teeth in their throat, as the chub or cheven, 

 and so the barbel, the gudgeon, the carp and divers others 

 have." The teeth are borne on a pair of strong, sickle-shaped 

 lower pharyngeal bones (Fig. 540), and, instead of meeting the 

 upper pharyngeals as in other fishes, they bite against a horny 

 pad at the base of the skull. The teeth are arranged in one, 

 two, or three rows, the principal row containing four to seven 

 teeth, the others one to three. The form of the individual 

 teeth varies greatly in the different species, being pointed, 

 hooked at the tips, serrated, spoon-shaped, molar-like, etc., 

 according to the nature of the diet. As a general rule the 

 carnivorous species have hooked or pointed teeth, the vege- 

 tarians grinding molars. Sometimes the diet is a mixed one, 

 and the Carp (Cyprinus), although mainly a vegetable feeder, 

 will also eat worms, shrimps, insects, and smaller fishes, and 

 it is said that the Barbel (Barbus) will not refuse any sort of 

 animal or vegetable substance. Not a few species subsist largely 

 on a diet of mud, from which they are able to extract sufficient 

 nutriment in the form of decaying animal and plant matter. 

 The manner in which they take in a mouthful of mud, extract 

 the nutriment by a churning movement of the jaws, and finally 

 eject the residue, is remarkable, and must be familiar to all 

 who have observed Gold-fish feeding in an aquarium. 



In the group of marine fishes known as Stromateoids or 

 Butter-fishes {Stromateoidea) , whose food seems to consist mainly 

 of polyps, crustaceans, etc., the teeth in the jaws are minute, 

 but the gullet has a remarkable structure, forming a pouch 

 with thick muscular walls on which a number of little teeth are 

 developed. The Square-tail ( Tetragonurus) , living almost entirely 

 on jelly-fishes, has a similar muscular gullet, but, as might be 

 expected from the nature of the food, this is devoid of teeth. 



Before concluding this chapter it may be of interest to mention 

 a few remarkable "meals" which have come to light from time 

 to time. A few years ago a number of X-ray photographs of 

 fresh-water Eels (Anguilla) were taken, and among the curious 

 objects seen in the stomachs were bones of water birds and 

 voles, pieces of wood and metal, a steel spring, and a piece of 

 lead pencil. The Wels or Glanis [Silurus) of Europe normally 

 feeds on fishes, frogs, and crustaceans, but a case is on record 

 of a child being swallowed whole by one of these large Cat-fishes, 

 and they are said to drag down and devour birds swimming 

 at the surface. The Cod {Gadus) is another mixed feeder, and 



