According to Pliny (viii. 38) the dolphins which enter the Nile are armed with a knife-edged spur on the back to protect themselves from the crocodiles. Cuvier refers this allusion to the _Squalus centrina_ or _Spinax_ of Linnæus. The European ‘file-fish’ (_Balistes capriscus_), found in a fossil state, and still existing, though rare in British waters, remarkably shows the efficiency, beauty, and variety of that order’s armature. It pierces its enemy from beneath by a strong erectile and cirrated spine on the first anterior dorsal; the base of the spear is expanded and perforated, and a bolt from the supporting plate passes freely through it. When the spine is raised, a hollow at the back receives a prominence from the next bony ray, which fixes the point in an erect position. Like the hammer of a fire-piece at full cock, the spear cannot be forced down till the prominence is withdrawn, as by pulling the trigger. This mechanism, says the learned and experienced Professor Owen,[31] may be compared with the fixing and unfixing of a bayonet: when the spine is bent down it is received into a groove in the supporting plate, and thus it offers no impediment to swimming. [Illustration: FIG. 4.—1. SPEAR OF NARWHAL; 2. SWORD OF XIPHIAS; 3. RHINOCEROS-HORN; 4. WALRUS TUSKS.] [Illustration: FIG. 5.—NARWHAL’S SWORD PIERCING PLANK.] [Illustration: FIG. 6.—METAL DAGGERS WITH HORN CURVE.] The pugnacious and voracious little ‘stickleback’ (_Gasterosteus_) is similarly provided. The ‘bull-head’ (_Cottus diceraus_, Pallas[32]) bears a multibarbed horn on its dorsum, exactly resembling the spears of the Eskimos and the savages of South America and Australia. The yellow-bellied ‘surgeon’ or lancet-fish (_Acanthurus_) is armed, in either ocean, with a long spine on each side of the tail; with this lance it defends itself dexterously against its many enemies. The _Naseus fronticornis_ (Lacépède) bears, besides the horn-muzzle, trenchant spear-formed blades in the pointed and serrated tail. The sting-fish or adder-pike (_Trachinus vipera_) has necessitated amputation of the wounded limb: the dorsals, as well as the opercular spines, have deep double grooves in which the venomous mucous secretion is lodged—a hint to dagger-makers. The sting-rays (_Raia trygon_ and _R. histrix_[33]) twist the long slender tail round the object of attack and cut the surface with the strong notched and spiny edge, inflicting a wound not easily healed. The sting, besides being poisonous, has the especial merit of breaking off in the wound: it is extensively used by the savages of the Fiji, the Gambier, and the Pellew Islands, of Tahiti, Samoa, and many of the Low Islands.[34] These properties would suggest poisoned weapons which cannot be extracted. Such are the arrows of the Bushman, the Shoshoni, and the Macoinchi of Guiana, culminating in the highly-civilised stiletto of hollow glass. [Illustration: FIG. 7.—MÁDU OR MÁRU.]