Some of the raptatorial Deep-sea fishes have a stomach so distensible and capacious that it can receive a fish of twice or thrice the bulk of the destroyer (_Melanocetus_, _Chiasmodus_, _Saccopharynx_). Deglutition is performed in them not by means of the muscles of the pharynx, as in other fishes, but by the independent and alternate action of the jaws, as in Snakes. These fishes cannot be said to swallow their food, but rather draw themselves over their victim, in the fashion of an _Actinia_. Before the voyage of H.M.S. “Challenger,” scarcely thirty Deep-sea fishes were known. This number is now much increased by the discovery of many new species and genera; but, singularly, no new types of families were discovered: nothing but what might have been expected from our previous knowledge of this group of fishes. Modifications of certain organs, perfectly novel, and of the greatest interest, were found, as we shall see in the “Systematic Part;” but the most important results of this voyage are that the general character of the abyssal fish-fauna, the abundance of fishes, and the exact depths to which fishes may descend, have been ascertained. However, the statements of the depths at which the fishes collected by the “Challenger” were taken cannot be received without some critical examination of each individual species. No precaution was taken to keep the mouth of the dredge closed during its descent or ascent, and therefore it is quite within the limits of probability that sometimes fishes were accidentally enclosed within the dredge, whilst it was traversing the surface strata. And this has happened more than once; for it is quite certain that common surface fishes like _Sternoptyx_ and _Astronestles_, never ranged to a depth of 2500 fathoms. On the other hand, the majority of the fishes obtained offer sufficient evidence from their own organisation that they live on the bottom, and are unable to support themselves in the water at a certain distance from the bottom or surface; and, consequently, that they actually were obtained at the depth to which the dredge descended.