General principles of zoology . arranged be-tween or behind the sensory cells. The simplest-formedeye, therefore, appears as a pigment-spot in the epitheliumof the skin sharply circumscribed, provided with nerves,commonly also with a lens (Fig. 78). The Rods and Cones.—The sensory cell itself bearsusually at its peripheral end a projection, called the rhab-dom. The rhabdom is a sort of cuticular structure,probably serving also to collect the rays of light and totransform them into stimuli, and has, particularly in thevertebrates, a complicated structure, inasmuch as eachrhabdom consists of an
General principles of zoology . arranged be-tween or behind the sensory cells. The simplest-formedeye, therefore, appears as a pigment-spot in the epitheliumof the skin sharply circumscribed, provided with nerves,commonly also with a lens (Fig. 78). The Rods and Cones.—The sensory cell itself bearsusually at its peripheral end a projection, called the rhab-dom. The rhabdom is a sort of cuticular structure,probably serving also to collect the rays of light and totransform them into stimuli, and has, particularly in thevertebrates, a complicated structure, inasmuch as eachrhabdom consists of an inner and an outer portion. Here 154 GENERAL PRINCIPLES OF ZOOLOGY. also can be distinguished two kinds of rhabdoms, rods andcones (Fig. 79). The Optic Ganglion.—Before the optic nerve dividesinto the separate optic cells,it forms a swelling, the opticganglion, which either liesas a detached body outside ofthe eye, or fuses with the re-tina into a connected parts designated as re-ticular, the internal granular Of.
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1896
