The fishes of the deep sea, in fact, with only one or two exceptions, all belong to the Order Teleostei, the most modern and most highly differentiated order of the class, the families that are most fully represented being the Macruridæ and then the Ophidiidæ and Gadidæ, and the Berycidæ. At the limits of the katantic and abysmal zones, a large number of families of Teleosteans entirely disappear, and as we approach the deepest parts of the ocean, the number of fish that are found is considerably reduced. As Dr. Günther very wisely remarks, ‘this diminution in the number may be due to the difficulty of capturing fishes at great depths, a difficulty which increases in proportion to the depths at which the dredge is worked. But it must also be regarded as evidence of the actually diminished variety of fishes.’ It may be interesting to the reader to give Dr. Günther’s table of the number of species found at different depths, as it shows, among other things, the marked change that occurs in the character of the fauna in passing from the katantic to the abysmal zone. Between 100–300 fathoms, 232 species Between 300–500 fathoms, 142 species Between 500–700 fathoms, 76 species Between 700–1,500 fathoms, 56 species Between 1,500–2,000 fathoms, 24 species Between 2,000–2,900 fathoms, 23 species As regards the general character presented by the deep-sea fishes, I have already pointed out in the chapter dealing with the general characters of the deep-sea fauna, the peculiarities in the size of the eyes, the colours and markings of the body, and the texture of the bones and muscles. There are, however, a few more characters of which mention must be made. Notwithstanding the fact that all the abysmal fishes are carnivorous and must consequently be capable—in the great number of cases—of rapid and vigorous movement, the muscles of the trunk and tail are usually thin, and the fascicles loosely connected with one another. Deep-sea fish are not characterised by an absence of the swimming bladder. This organ occurs just as frequently and in the same families as in the shallow-water fauna, but we do not know whether it possesses any special peculiarities or not, as it is usually so ruptured and destroyed by the change of pressure it undergoes in being brought to the surface, that it is impossible to make any thoroughly accurate investigation of its anatomy and relations. The extraordinary development of glands in the skin which secrete mucus, and the presence in many forms of very highly specialised organs for emitting phosphorescent light, are characters of the deep-sea fish fauna, to which I have referred in a previous chapter.