Adaptations of Fishes 73 
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 Guinea, Pristi- 
ophorus in Japan and Australia. In the mythology of science, the 
Fie. 55.—Saw-shark, Pristiophorus japonicus 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 excessively 
small and toothless, at the end of a long tube, so ineffective in 
appearance that it is a marvel that the fish can swallow any- 
thing at all. 
In the thread-eels (Nemichthys) the jaws are so recurved 
that they cannot possibly meet, and in their great length seem 
worse than useless. 
In some species the knife-like 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 horny beak like that of 
the parrot. These are the Chimeras, the globefishes (Tetroadon), 
and their relatives, the parrot-fishes (Scarus, etc.), and the 
stone-wall perch (Oplegnathus). 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 
