"It has been observed," says Yarrell, "that when a shark and his pilot were following a vessel, if meat was thrown overboard cut into small pieces, and therefore unworthy the shark's attention, the pilot-fish showed his true motive of action by deserting both shark and ship to feed at his leisure on the morsels."
The family of the anguilliform fishes, characterised by their serpent-like bodies, destitute of ventral fins, and generally covered by a slippery skin, with, in some of the genera, small scales embedded therein, likewise comprises a number of highly interesting and useful species, forming many generic groups.
Its chief representative in our waters is the Common Eel (_Anguilla vulgaris_), which, though a frequent inhabitant of our lakes, ponds, and rivers, may also justly be reckoned among the marine fishes; for the same wonderful instinct which prompts the salmon and the sturgeon annually to leave the high seas and seek the inland streams for the sake of perpetuating their race, forces also the eel to migrate, but his peregrinations are of an opposite character, for here the full-grown fishes descend the rivers to deposit their spawn in the sea, and the young, after having been born in the brackish estuaries, ascend the streams to accomplish their growth in the sweet waters. The mode of procreation of eels, which for ages had been an enigma, has now at length been completely elucidated by Professor Rathke, who discovered that the eggs, which are of microscopic smallness, so as to be undistinguishable by the naked eye from the fat in which they lie imbedded, are expelled through an opening hardly large enough to admit the point of a needle. The energy of the salmon in swimming stream-upwards for hundreds and hundreds of miles, and bounding over rapids and cataracts, is truly wonderful, but the instinctive efforts of the little eels or _elvers_ to surmount obstacles that seem quite out of proportion to their strength are no less admirable. Mr. Anderson, upwards of a century ago, described the young eels as ascending the upright posts and gates of the waterworks at Norwich until they came into the dam above; and Sir Humphry Davy, who was witness of a vast migration of elvers at Ballyshannon, speaks of the mouth of the river under the fall as blackened by millions of little eels. "Thousands," he adds, "died, but their bodies remaining moist, served as the ladder for others to make their way; and I saw some ascending even perpendicular stones, making their road through wet moss, or adhering to some eels that had died in the attempt. Such is the energy of these little animals that they continue to find their way in immense numbers to Loch Erne. Even the mighty fall of Schaffhausen (which stops the salmon) does not prevent them from making their way to the Lake of Constance, where I have seen many very large eels." After the little eels have gained the summit of a fall, they rest for a while with their heads protruded into the stream. They then urge themselves forward, taking advantage of every projecting stone or slack water, and never get carried back by the current. Myriads are destroyed on the way by birds or fishes; but, as usual, their greatest enemy is man, who not only devours whole cart-loads of little eels not larger than a knitting-needle, frying them into cakes, which are said to be delicious, though rather queer-looking from the number of little eyes with which they are bespangled, but after getting tired of eating them, actually feeds his pigs with them, or even uses them for manure. A prodigal waste which should be looked after, as these little eels would soon increase their weight, and consequently their value a thousand fold. On the Continent many lakes and ponds have been stocked with elvers, packed in wet grass, and sent by the railroads or the post far into the interior of the country.