MOUTHS AND JAWS 115 



even been suggested that the sword has not been evolved 

 as a weapon at all, but merely represents an extreme case 

 of stream-lining, the pointed rostrum acting as an efficient 

 cutwater. 



In some fishes the anterior part of the head is drawn out, 

 but the mouth itself remains small and is placed at the ex- 

 tremity of a long, tube-like beak. Among the Mormyrids 

 (Mormyridae) of the fresh waters of Africa, for example, a 

 number of diverse modifications of the snout are encountered. 

 In the Elephant Mormyrid {Gnathonemus) this takes the form 

 of a curved, trunk-like structure, at the tip of which is the 

 tiny mouth armed with few but relatively large teeth (Fig. 47A) . 

 This remarkable appendage is used for inserting between stones 

 or into the mud in search of small crustaceans and the like 

 which form the principal food. These fishes live mostly in 

 more or less muddy water, and the eyes are consequently small 

 and often much degenerated. In some species the lower lip is 

 provided with a fleshy mental appendage, which may be 

 globular in shape or take the form of a membranous tassel; 

 this is sensitive, and acts as an organ of touch, aiding in the 

 search for food and compensating for the imperfect vision. 

 Similar modifications of the snout and jaws are found among 

 the Gymnotids of South America. In the tribe of Butterfly- 

 fishes (Chaetodontidae), nearly all inhabitants of coral reefs, many 

 of the species have the mouth placed at the end of a straight, 

 tubular snout, and this is used for poking into crevices and 

 holes in the coral in search of prey (Fig. 47F). 



The members of the large and varied order of Tube-mouths 

 {Solenichthyes) all agree in having the snout prolonged to form 

 a rigid tube-like "beak," with a small mouth at its extremity 

 (Fig. 49A). The jaws themselves are quite short, and in order 

 that they may be articulated with the hinder part of the skull 

 in the usual manner the suspensory part of the hyoid arch, the 

 hyomandibular bone, is drawn out into a long, rod-like structure. 

 The Trumpet-fishes (Fistulariidae) and their allies have some 

 minute teeth in the mouth, but these are wanting in all the 

 other members of the order. The Pipe-fishes [Syngnathidae) live 

 almost entirely on small crustaceans, and when searching for 

 food they swim about slowly in a most curious manner, holding 

 the body now in a vertical and now in a horizontal position, 

 and indulging in wriggles and contortions of every conceivable 

 kind. The head is in constant movement, the long snout being 

 poked into clumps of vegetation or into any other situation 



