Of all the branches of study into which natural history has been divided, the most interesting, from its extensiveness, its variety, and the almost insurmountable difficulties which it presents to the student, is Ichthyology. To acquire a thorough knowledge of zoology requires much labour, study, travel, and considerable risk; in like manner with ornithology, in the prosecution of which the difficulties are greater, from the mixture of elements; but still the inhabitants of the air have thus much in common with us, that they live in the same atmospheric medium, derive their sustenance from the same earth, and although the difficulties of following their motions, and observing (unseen by them) their habits and natures, are considerable, yet still, thanks to the extension of science, they have not proved unconquerable, and the telescope, in that form called the ornithoscope, has enabled man to acquire a large store of information on this interesting subject. But with ichthyology how widely different! Here the preliminary obstacle which presents itself is an element fatal to the existence of man within it, and out of which the creatures with whose nature he would fain be acquainted cannot exist. His very powers of observation are thus rendered useless, except in a very limited degree. They are bounded by a glass vase, or a small clear pond at the utmost, and confined to a few specimens of the smaller fishes, and even then it is doubtful whether circumstances may not have altered their really natural habits. Yet above these obstacles the mind of man has risen, and by the union of analogy with laborious and constant observation, he has succeeded in classing a large amount of the tenants of the mighty deep. But before he can ascertain what proportion, or write the history of any one of them fully, he must discover some substitute for gills which will enable him to extract the necessary air for his existence from the water, and thus enable him to search the depths of ocean, and seek its inhabitants in their haunts. That such may yet be discovered by the ingenuity of man, let no one deem impossible.