short columns standing up in relief from its basal membrane.’ Each hexagonal column is composed of a number of transparent rods disposed side by side at right angles to the outer surface of the organ, with their bases applied against the concave surface of a large hexagonal pigment cell, one of which forms the basis of each hexagonal column. It is still very doubtful what are the true homologies of this extraordinary phosphorescent organ, but Moseley was of opinion that, ‘on the whole, it seems not unlikely that the remarkable head organs of Ipnops may be regarded as highly specialised and enormously enlarged representatives of the phosphorescent organs on the heads of such allied Scopelidæ as _Scopelus rafinesquii_ and _Scopelus metopoclampus_. It may be conceived that in _Ipnops_ the supra-nasal and sub-ocular phosphorescent organs of these species on either side have united and become one with the result of the total obliteration of the eye.’ Most of the species of the genus _Scopelus_ are undoubtedly pelagic in habit, descending during the day to depths of semi-darkness but rising at night to the surface waters. It is not certain how many of the known species occasionally or habitually dwell in very deep water, but there seems to be no doubt that two species at least—_S. macrolepidotus_ and _S. glacialis_—belong to the abysmal zone. Both of these species were found in dredges that had been at work in depths of over 1,000 fathoms and showed signs when examined of having been brought from the abyss. The Stomiatidæ are almost entirely confined to water from 450 to nearly 2,000 fathoms in depth. They may be distinguished from the Scopelidæ by the long hyoid barbel close to the symphysis of the lower jaw, but like many of the genera of that family they have wide gaping mouths armed with a profusion of vicious looking teeth and a series of luminous spots on the sides of the head and body. (_See_ Frontispiece.) In _Eustomias obscurus_, found in depths of over 1,000 fathoms in the Atlantic by the ‘Talisman,’ the barbel is provided with a terminal swelling, shaped like a dumb-bell, which may be capable of emitting a phosphorescent light and serve the animal as a lure for the attraction of its prey. The genus _Malacosteus_, too, presents us with some of the most remarkable forms that are found in the abysmal zone. The mouth is of enormous size and the integuments of the abdomen present very definite longitudinal folds, leaving no doubt that this fish is able, like several others living in deep water, to swallow prey of an enormous size.