. Comparative animal physiology. Physiology, Comparative; Physiology, Comparative. 390 Comparative Animal Physiology rhabdom of the crystaline cone through which the hght has passed. There fore, there are two possible types of image formation, as shown in Figure 106. In A is shown the so-called apposition image, in which each rhabdom receives light which enters the ommatidium parallel to its axis. In this type the length of the crystalline cone may be equal to its focal length, as in Figure 105, A. In B is shown an image formed by superposition, in which light from a point (e) may pass through
. Comparative animal physiology. Physiology, Comparative; Physiology, Comparative. 390 Comparative Animal Physiology rhabdom of the crystaline cone through which the hght has passed. There fore, there are two possible types of image formation, as shown in Figure 106. In A is shown the so-called apposition image, in which each rhabdom receives light which enters the ommatidium parallel to its axis. In this type the length of the crystalline cone may be equal to its focal length, as in Figure 105, A. In B is shown an image formed by superposition, in which light from a point (e) may pass through any of a number of crystalline cones and be bent (as in Figure 105, B), so that it is focused on a single. Fig. 105. Diagram of the two types of ommatidium. A, From eye forming apposition image (after Snodgrass); B, From eye forming superposition image (after Weber), a, Corneal lens; h, matrix cells of cornea; c, crystalline cone; d, iris pigment cells; e, rhabdom; f, retinal cells; g, retinal pigment cells; h, fenestrated basement membrane; i, eccentric retinal cell; k, translucent filament connecting crystalline cone with rhabdom; I, nerve fibers. From Wiggles worth ."^ rhabdom. In this type the length of the crystalline cone is twice the focal length. If the secondary iris pigment should migrate, as shown in Figure 105, B, then the superposition eye may function as an apposition eye. In general, most diurnal insects have apposition eyes, and nocturnal ones have superposition eyes. Undoubtedly there are many intermediate types. In some insects the cone cells are not refractile and apparently do not serve as lenses. The apposition eye is adapted to function at high light intensity and is really very inefficient as a light-gathering device. The superposition eye is adapted to low light intensities and is much more efficient for gathering light than the apposition eye, but is still much less efficient than most vertebrate eyes. Because of the fact that the image formed by
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