MOUTHS AND JAWS 117 



where the prey is Hkely to be encountered. The actual manner 

 of feeding is remarkable, the tube-like "beak" acting as a 

 kind of syringe, the prey being drawn in rapidly by inflating 

 the cheeks. The Sea Horses [Hippocampus) have a similar diet, 

 which seems to be obtained in a like manner. The fish will 

 approach a small crustacean in a leisurely manner, peer at it 

 for a second or two, and then, having placed its snout in a 

 convenient position, suddenly engulf the meal. 



In a number of fishes the mouth is described as protractile; 

 that is to say, it can be protruded or withdrawn at will. In the 

 Sturgeon (Acipenser) the funnel-like mouth is thrust downward 

 by a forward or backward swing of the suspensory bones of the 

 hyoid arch, but in most other fishes the protrusion is accom- 

 plished by the praemaxillaries of the upper jaw sliding on 

 certain bones of the front part of the skull, the small maxillaries 

 acting after the manner of levers. In many members of the 

 Carp tribe {Cyprinidae) the mouth is especially protractile, and 

 in the Bream (Abramis), for example, forms a sort of tube when 

 protruded. The John Dory (^eus), with its large and very 

 protractile mouth and mournful expression, has an interesting 

 method of hunting the small fishes on which it feeds. Its deep 

 and clumsy body is unsuited for chasing prey, but when swim- 

 ming upright in mid-water its excessive thinness makes it quite 

 inconspicuous, and when placed end-on towards the victim 

 it is almost invisible and excites no alarm. In this way it is 

 able to approach gradually until within striking distance, 

 when the jaws are shot forward with great rapidity (Fig. 49B). 

 During the preliminary manoeuvres the whole attitude of the 

 Dory is one of suppressed excitement, and the eyes are kept 

 fixed intently on the prospective victim. Among the Wrasses, 

 one tropical form known as Epibulus has the mouth even more 

 protrusible than that of the John Dory. In the latter only the 

 upper jaw is thrust forward, but in Epibulus the lower jaw is 

 also moved, the bone to which it is articulated being long and 

 movable, a condition quite unlike that of the other Wrasses in 

 which it is quite short and firmly fixed (Fig. 49c). 



The order of fishes (Allotriognathi) , including the Opah 

 (Lampris), Deal-fish (Trachypterus) , and Ribbon-fish [Regalecus] 

 contains some strange and very diverse forms, but all agree in 

 the mechanism of the jaws. In other fishes with protractile 

 mouths only the end of the maxillary bone moves forward 

 when the mouth is opened, the other end being fixed, but in 

 the members of this group the maxillary of each side is thrust 



