. The depths of the ocean; a general account of the modern science of oceanography based largely on the scientific researches of the Norwegian steamer Michael Sars in the North Atlantic. Oceanography. GENERAL BIOLOGY 675 single row of luminous cells in the usual epithelium, and a lens formed by the cuticula or chitinous layer of the epidermis. In squids and fishes the organs are very complicated, as we shall presently see. The object of the " Michael Sars " Expedition being mainly the investigation of the distribution of animals, the examination of the collections has necessarily bee
. The depths of the ocean; a general account of the modern science of oceanography based largely on the scientific researches of the Norwegian steamer Michael Sars in the North Atlantic. Oceanography. GENERAL BIOLOGY 675 single row of luminous cells in the usual epithelium, and a lens formed by the cuticula or chitinous layer of the epidermis. In squids and fishes the organs are very complicated, as we shall presently see. The object of the " Michael Sars " Expedition being mainly the investigation of the distribution of animals, the examination of the collections has necessarily been limited to the determina- tion of the species, and my contributions to this fascinating section of the science of marine life will largely consist in dis- cussing the distribution of animals possessing light-organs, which occur in salt water only, for no luminous animals are known from fresh water and no phosphorescence occurs there. Glandular, clearly defined, and localised light-organs are Light-organs found mainly in pelagic animals. Among bottom animals p0HnCipaiiy from the coast banks luminosity is exceed- in pelagic ingly rare, but on the other hand, many bottom animals have been brought up from the abyssal region in a luminous condition, and have continued to emit light when placed in dark surroundings c?.._ on board (see Fig. 70, p. 88, representing a luminous umbellularian). No special luminous structure has been found in these cases, the luminosity being attached Light-organ of sergestes chai- to the surface epithelium. As regards SAt^.ln^ fishes, Giinther has drawn attention to lens; d, glandular ceils; the fact that many deep-sea forms secrete HaLen^from steuer.) a large amount of slime. The heads of many deep-sea Macruridae exhibit certain pits and channels, which produce great quantities of slime. This slime is supposed to be luminous, and to perform the function of ordinary glan- dular light-organs, which last are found only in a few fishes sup- posed to live a
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