Adaptations of Fishes 201 



right and left with this saw, destroying the small fishes, who 

 thus become an easy prey. These fishes live in estuaries and 

 river mouths, Pristis in tropical America and Gruinea, Pristi- 

 ophorns in Japan and Australia. In the mythology of science, the 



Fig. 153. — Saw-shark, Pristiophorus ja-ponicvs Giinther. Specimen from 



Nagasaki. 



sawfish attacks the whale, but in fact the two animals never 

 come within miles of each other, and the sawfish is an object of 

 danger only to the tender fishes, the small fry of the sea. 



Peculiarties of Jaws and Teeth. — The jaws of fishes are sub- 

 ject to a great variety of modifications. In some the bones are 

 joined by distensible ligaments and the fish can swallow other 

 fishes larger than itself. In other cases the jaws are excessi\-ely 

 small and toothless, at the end of a long tube, so ineft'ective m 

 appearance that it is a mar\'el that the fish can swallow any- 

 thing at all. 



In the thread-eels (Nemichthys) the jaws are so recurA-ed 

 that they cannot possibly meet, and in their great length seem 

 worse than useless. 



In some species the knife-Hke canines of the lower jaw pierce 

 through the substance of the upper. 



In four different and wholly unrelated groups of fishes the 

 teeth are grown fast together, forming a homy beak like that of 

 the parrot. These are the Chimasras, the globefishes (Tciroadoii), 

 and their relatives, the parrot-fishes (Scants, etc.), and the 

 stone-wall perch (OplegnatJms). The structure of the beak 

 varies considerably in these four cases, in accord with the dif- 

 ference in the origin of its structures. In the globefishes the 



