. 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. "Michael Sars" North Atlantic Deep-sea Expedition (1910); Oceanography; North Atlantic Ocean. 684 DEPTHS OF THE OCEAN an Argyropelecus seen from above, and we see that the eyes point upwards, which is probably the case in most fishes possessing telescopic eyes, even if exceptions occur. Two interesting facts go to explain this peculiar adaptation. Firstly, these telescopic eyes occur only in fishes
. 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. "Michael Sars" North Atlantic Deep-sea Expedition (1910); Oceanography; North Atlantic Ocean. 684 DEPTHS OF THE OCEAN an Argyropelecus seen from above, and we see that the eyes point upwards, which is probably the case in most fishes possessing telescopic eyes, even if exceptions occur. Two interesting facts go to explain this peculiar adaptation. Firstly, these telescopic eyes occur only in fishes which are very bad swimmers, fishes which practically only float in the water-layers. Secondly, the light-measurements in the Sargasso Sea showed that the light-rays acted more strongly on the top plate than on the side plates ; for fishes possessing small swimming capacity the telescopic eyes seem to be most perfectly adapted to receive the faint rays of light which penetrate to these dusky depths. Among eyes built on the general principle the difference in size first com- mands attention when the vertical pene- tration of light and the vertical distribution of each species come to be investigated. As regards the upper layers, an interest- ing subject will also be found in the detailed study of the anatomy of dif- ferent eyes. In the retina of the human eye two special kinds of sensory cells are known to occur, viz. "rods" and "; These cells occur also in the eyes of fish from the surface layers. From Brauer's investigations we know that in all deep-sea fishes, as well as in silvery fishes from about 300 metres, only the " rods " are found in the retina of the eye. According to an old maxim of Max Schultze, nocturnal animals possess only "rods" while diurnal animals have both It has therefore been generally believed that the "rods" alone possess the faculty of observing light-intensity, light and shade, while only the &qu
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