They employ only three months in ascending to the sources of the Maragnon (a journey of 3,000 miles), the current of which is remarkably rapid, which is at the rate of nearly forty miles a day; in a smooth stream or lake their progress would increase in a fourfold ratio. Their tail is a very powerful organ, and its muscles have wonderful energy; by placing it in their mouths they make of it a very elastic spring, for letting it go with violence they raise themselves in the air to the height of from twelve to fifteen feet, and so clear the cataract that impedes their course: if they fail in their first attempt, they continue their efforts till they have accomplished it.[124] _General Intelligence._ With reference to the general intelligence of fish, allusion may first be made to their marked increase of wariness in waters which are much fished. This shows no small degree of intelligence, for the caution is proved to be the result of observation by the fact that young trout under such circumstances are less wary than old ones. Moreover, many fish will abandon old haunts when much disturbed. Again, according to Kirby, the carp thrusts itself into the mud in order that the net may pass over it, or, if the bottom be stony, makes great leaps to clear it. At the Andaman Islands fish are captured by the convicts by means of weirs fixed across the openings of creeks. After existing a week or so, it is observed that captures invariably cease; and it is believed that such is due to barnacles, &c., clustering on to the wood of which they are composed. It does not seem improbable that the fish have learned to avoid a locality out of terror at those which enter but do not again return.[125] Lacepède[126] relates that some fish, which had been kept for many years in a basin of the Tuileries, would come when called by their names. Probably it was the sound of the voice and not the articulate words to which they responded; for Lacepède also relates that in many parts of Germany trout, carp, and tench were summoned to their food by the sound of a bell; and the same thing has been recorded of various fish in various localities, notably by Sir Joseph Banks, who used to collect his fish by sounding a bell.[127] In 'Nature' (vol. xi., p. 48) Mr. Mitchell gives the following instance of intelligence on the part of a small perch. Having one day disturbed its nest full of young fry, Mr. Mitchell next day went to look for the nest; 'but we searched in vain for the fish and her young. At length, a few yards further up stream, we discovered the parent guarding her fry with jealous care in a cavity scooped out of the coarse sand. . . . This is the first and only instance that has come under my notice of a fish watching over her young, and conveying them, when threatened with danger, to some other place.'