. The crayfish; an introduction to the study of zoology. Crayfish; Zoology. THE THEORY OF MOSAIC VISION. 123 Each visual pyramid, isolated from its fellows by its coat of pigment, may be supposed, in fact, to play the part of a very narrow straight tube, with blackened walls, one end of which is turned tow^ards the external world, while the other incloses the extremity of one of the nerve fibres. The only light which can reach the latter, under these circum- stances, is such as proceeds from points which lie in the. 2*-- FiG. 29.—Diagram showing the course of rays of light from three points X,
. The crayfish; an introduction to the study of zoology. Crayfish; Zoology. THE THEORY OF MOSAIC VISION. 123 Each visual pyramid, isolated from its fellows by its coat of pigment, may be supposed, in fact, to play the part of a very narrow straight tube, with blackened walls, one end of which is turned tow^ards the external world, while the other incloses the extremity of one of the nerve fibres. The only light which can reach the latter, under these circum- stances, is such as proceeds from points which lie in the. 2*-- FiG. 29.—Diagram showing the course of rays of light from three points X, y, z, through the nine visual rods (supposed to be empty- tubes) A—I of a compound eye ; a—i, the nerve fibres connected with the visual rods. direction of a straight line represented b}' the produced axis of the tubes. Suppose A—I to be nine such tubes, a—i the corre- sponding nerve fibres, and x y z three points from which hght proceeds. Then it will be obvious that the only light. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Huxley, Thomas Henry, 1825-1895. New York, D. Appleton and company
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Keywords: ., bookauthorhu, bookcentury1800, bookdecade1880, booksubjectzoology
