THE TRIGGER-FISH 



with median and unpaired fins, they are certainly not 

 so well equipped with paired fins. The pelvic fins 

 are replaced by a pointed tubercle. The pectoral fins 

 are small and short, but make up for their size by 

 affording a capacity for movement not possessed by 

 other fish. Usually, in these other fishes, the pectoral 

 fins can move from above downward and backward, 

 but not forwards. Their movements are conse- 

 quently limited, the articulations being of restricted 

 capacity. This is not so in the trigger-fish, which can 

 move these fins ■ forward. Sometimes, if we watch 

 these creatures moving about in an aquarium, we may 

 see the curious phenomenon of a fish bringing its 

 pectoral fins over towards its eyes, as the higher 

 vertebrates do their arms, and covering a part of the 

 cheeks. This indicates a perfection of articulation 

 of which we have another and better example in the 

 rays of the front dorsal fin. 



There are three of these rays. The first and strongest, 

 a solid point bristling with spines from the base to the 

 top on its front side, is succeeded at a little distance 

 by the second, smaller, smooth, sloping like a buttress; 

 the third, smaller still and further off, is entirely behind. 

 All three, so far as their action is concerned, are closely 

 connected one with another. The fin is able to close 

 up in its groove or to erect itself; it is possible, when 

 the animal is alive, to stretch it out without any diffi- 

 culty by raising the first ray; but it is impossible to 

 do the opposite, and fold the whole wing back again 

 in its groove by pressing on it. A fisherman can always 

 prove this to you. This particular dorsal ray, once 

 extended, remains motionless, its spines projecting, 

 quite different from anything we notice elsewhere. 

 We might have to break the first ray before we could 

 lower it. Firmly wedged, it resists all efforts. But 

 we can lower the second, or the third, ray and so 

 secure the desired end without trouble; the fin closing 

 up completely. 



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