. A manual of zoology. Zoology. GENERAL ORGANOLOGY 121 the cornea. Internally to the sclera lies the chorioidea, which, at the junction of sclera and cornea, is changed into the iris. Tlie iris, the seat of the color of the e)-e, is pierced by the pupil, which regulates the amount of light. Next internal to the chorioid follows a layer of black cells, the tapelum nignim (pig- mented epithelium), and finally the retina itself, the expansion of the optic nerve which enters the eye at the hinder part. The tapetum nigrum and the retina arise together, and hence both end at the edge of the pupil, a
. A manual of zoology. Zoology. GENERAL ORGANOLOGY 121 the cornea. Internally to the sclera lies the chorioidea, which, at the junction of sclera and cornea, is changed into the iris. Tlie iris, the seat of the color of the e)-e, is pierced by the pupil, which regulates the amount of light. Next internal to the chorioid follows a layer of black cells, the tapelum nignim (pig- mented epithelium), and finally the retina itself, the expansion of the optic nerve which enters the eye at the hinder part. The tapetum nigrum and the retina arise together, and hence both end at the edge of the pupil, although the retina loses its nervous character at the ora serrata, some distance from the outer edge of the iris. The cavity of the eye is completely filled by the vitreous body, aqueous humor, and the lens. For vision the lens is the most important, since, next to the cornea, it influences most the course of the rays of light. It lies behind the iris, fixed to the anterior wall of the chorioid, which here is changed into the ciliary process. In front of it is a serous fluid, the aqueous humor, partly in the so-called posterior chamber of the eye, between the lens and iris, partly in the anterior chamber, between the iris and cornea. The single, larger cavity behind the lens is filled up by a jelly-like vitreous body. The image formed on the retina is in- verted. Shining of Eyes.—In many verte- brates there is a tapetum lucidum. inside the chorioid which causes the so-called shining of eyes (cats). This is a layer, which reflects light so strongly that only a little light from the outside is necessary to illumine the back of the eye. There is no real production of light. The tapetum nigrum must be free from pigment in order that the tapetum lucidum may act. In many insects and spiders light is sim- ilarly reflected from the back of the eye. Phosphorescent Organs.—For a long time eye-like organs have been known, especially in animals from the deep seas (fishes, cephalopods,
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectzoology, bookyear1912
