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ing in a minute hook. A fibrous structure is seen to 

 run diagonally across the blade, the edge of which is 

 set with minute barbs pointing outwards, resembling 

 very fine and very short bristles. The whole bundle 

 is connected with a long slender rod of cartilage, which, 

 doubtless acted upon by proper muscles, moves to and 

 fro through the muscular sheath, protruding the bundle 

 of bristles, or entirely retracting them within the body. 

 The bristles, when protruded, slightly diverge, so that 

 the dilated blades of these hundred oars strike with full 

 force upon the water in rowing, if such indeed is the 

 nature of their action, as some have supposed. In the 

 act of withdrawal, however, into the narrow compass 

 of the muscular sheath, the blades slide one upon 

 another, so as to present a surface considerably di- 

 minished. But why is each bristle hooked and barbed ? 

 The obvious supposition is that these organs act like 

 the pole of a ferry-boat in the shallows ; the barbs, 

 pointing outwards, serving to catch any roughness of 

 the surface, and thus to push the animal by their 

 resistance, while the terminal hook may serve to pull 

 in an analogous manner. But then the barbed and 

 hooked edge is the upper one of each oar, a circum- 

 stance which renders such an explanation at first sight 

 unsatisfactory. Perhaps, however, the habit of the 

 animal of living under stones, may in some measure 



