Adaptations of Fishes 5 
vertically styliform and very mobile. It is armed behind with 
a spine eight lines long and of the same form as the hollow 
venom-fang of a snake, being perforated at its base and at its 
extremity. A sac covering the base of the spine discharges its 
contents through the apertures and the canal in the interior of 
the spine. The structure of the dorsal spines is similar. There 
are no secretory glands imbedded in the membranes of the sacs 
and the fluid must be secreted by their mucous membrane. The 
sacs are without an external muscular layer and situated im- 
mediately below the thick, loose skin which envelops the spines 
at their extremity. The ejection of the poison into a living 
animal, therefore, can only be effected as in Synanceia, by the 
pressure to which the sac is subjected the moment the spine 
enters another body.” 
The Lancet of the Surgeon-fish.—Some fishes defend themselves 
by lashing their enemies with their tails. In the tangs, or surgeon- 
fishes (Teuthis), the tail is provided with a tormidable weapon, 
Fig 37.—Brown Tang, Teuthis bahianus (Ranzani). Tortugas, Florida. 
a knife-like spine, with the sharp edge directed forward. This 
spine when not in use slips forward into a sheath. The fish, 
when alive, cannot be handled without danger of a severe cut. 
In the related genera, this lancet is very much more blunt 
and immovable, degenerating at last into the rough spines of 
Balistapus or the hair-like prickles of Monacanthus. 
