Journal of comparative neurology . le. The eye (fig. A, oc), which lies just bene<ath the surfaceepithelium, has the shai:)e of a cone or pear whose base, cor-responding to the corneal portion, points outward. The basehas a diameter of about 150 m, whereas the axial measurementis 200 M- An axial section of the eye (fig. B) shows the following parts :(1) optic capsule; (2) cornea; (3) retina; (4) optic nerve; (5)lens; (6) vitreous humor. The optic capsule (fig. 3, cps. opt.) is a thin, connective-tissue sheath surrounding the eye, to which the retinal and cor-neal elements are attached. It i
Journal of comparative neurology . le. The eye (fig. A, oc), which lies just bene<ath the surfaceepithelium, has the shai:)e of a cone or pear whose base, cor-responding to the corneal portion, points outward. The basehas a diameter of about 150 m, whereas the axial measurementis 200 M- An axial section of the eye (fig. B) shows the following parts :(1) optic capsule; (2) cornea; (3) retina; (4) optic nerve; (5)lens; (6) vitreous humor. The optic capsule (fig. 3, cps. opt.) is a thin, connective-tissue sheath surrounding the eye, to which the retinal and cor-neal elements are attached. It is continuous with the sheathof the optic nerve. 366 LESLIE B. AREY The cornea and retina represent differentiated portions ofan original sac-like epithelial invagination (figs. A and B).The wall of this closed optic sac/ as it is called, never becomesmore than one cell thick. The pigment-free corneal cells areonly slightly columnar in shape, hence this portion of the opticsac remains as a thin membrane, which is strikingly in con-. Fig. B An axial section (semi-diagrammatic) of an entire eye of Planorbis(X 275). cm., cornea; hu. vit., vitreous humor; Ins., lens; nl. cl. rtn., nucleusof retinal cell; n. opt., optic nerve; pr^., pigment; rtn., retina. trast with the thick cornea of some other pulmonates. Itsextent is limited to the broad base of the conical eye (fig. B). The retinal portion of the optic sac is easily distinguishablefrom the cornea by the presence, in the former, of pigmentedcells and by the great elongation of all its elements (figs. B andC). In general, the constituent cells maj^ be said to have aradial arrangement with respect to the optic sac. Notwith-standing the fact that the retina is only one cell thick, it is con- RETINAL PIGMENT OF PLANORBIS 367 venient to follow the suggestion of Smith (06) and distinguishthree concentric zones, which, although of an arbitrary nature,are on the whole rather clearly defined. The peripheral zone(fig. C, rtn. ex.) is in co
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Keywords: ., bookauthorw, bookcentury1900, bookdecade1910, booksubjectmedicine
