I fear that before many years have elapsed the Sirens of the Naturalist will have disappeared from our earth, before the advance of civilization, as completely as the fables and superstitions with which they have been connected, before the increase of knowledge; and that the mermaid of fact will have become as much a creature of the past as the mermaid of fiction. With regard to the latter--the Siren of the poets,--the water-maiden of the pearly comb, the crystal mirror, and the sea-green tresses,--there are few persons I suppose, at the present day who would not be content to be classed with Banks, the fine old naturalist and formerly ship-mate of Captain Cook. Sir Humphry Davy in his _Salmonia_ relates an anecdote of a baronet, a profound believer in these fish-tailed ladies, who on hearing some one praise very highly Sir Joseph Banks, said that "Sir Joseph was an excellent man, but he had his prejudices--he did not believe in the mermaid." I confess to having a similar "prejudice;" and am willing to adopt the further remark of Sir Humphry Davy:--"I am too much of the school of Izaac Walton to talk of impossibility. It doubtless might please God to make a mermaid, but I don't believe God ever did make one." THE LERNEAN HYDRA. The mystery of the Kraken, of which I treated in a companion volume to the present, recently published, is not difficult to unravel. The clue to it is plain, and when properly taken up is as easily unwound, to arrive at the truth, as a cocoon of silk, to get at the chrysalis within it. It was a boorish exaggeration, a legend of ignorance, superstition, and wonder. But when such a skein of facts has passed through the hands of the poets, it is sure to be found in a much more intricate tangle; and many a knot of pure invention may have to be cut before it is made clear. Nevertheless, we shall be able to discern that more than one of the most famous and hideous monsters of old classical lore originated, like the Kraken, in a knowledge by their authors of the form and habits of those strange sea-creatures, the head-footed mollusks. There can be little doubt that the octopus was the model from which the old poets and artists formed their ideas, and drew their pictures of the Lernean Hydra, whose heads grew again when cut off by Hercules; and also of the monster Scylla, who, with six heads and six long writhing necks, snatched men off the decks of passing ships and devoured them in the recesses of her gloomy cavern. Of the Hydra Diodorus relates that it had a hundred heads; Simonides says fifty; but the generally received opinion was that of Apollodorus, Hyginus, and others, that it had only nine.