An introduction to the study of the comparative anatomy of animals . ntinued into a fibril of theolfactory nerve. The rods and cones of the retina are peculiar structures,each being a product of rather than a metamorphosedepithelial cell. A rod is a cylindrical rod-shaped bodyabout oo5 mm. in length, consisting of two parts, a longer,highly refractive, outer limb, and a shorter, more homogeneous,less refractive, inner limb, separated by a small plano-convexstructure known as the lenticular body (fig. 15, C). At thebase of each rod is an oval nucleus surrounded by a very thinsheath of granular
An introduction to the study of the comparative anatomy of animals . ntinued into a fibril of theolfactory nerve. The rods and cones of the retina are peculiar structures,each being a product of rather than a metamorphosedepithelial cell. A rod is a cylindrical rod-shaped bodyabout oo5 mm. in length, consisting of two parts, a longer,highly refractive, outer limb, and a shorter, more homogeneous,less refractive, inner limb, separated by a small plano-convexstructure known as the lenticular body (fig. 15, C). At thebase of each rod is an oval nucleus surrounded by a very thinsheath of granular protoplasmic matter which is continued inter- Digitized by Microsoft® HISTOLOGY OF THE FROG 89 nally as a fine fibril; this probably becomes continuous with,or comes in contact with, a terminal fibril of the optic nerve. Hair-cells from the crista acustica of an ampulla of the earare shown in fig. 15, -5. Each is a pyriform cell, the narrowerend turned towards the cavity of the ampulla, and bearingon its truncated free surface a long stiff hair-like process which. Various forms of sensory epithelium. ^, two forked cells from the tongueof the frog ; B, B, two forms of auditory hair cells from the cristaacustica of the anterior ampulla of the frogs ear ; C, three rods and acone from the retina of the frogs eye ; D, two olfactory cells, withtheir epithelial supporting cells from the frogs nose. (All the figuresafter Haslam in Eckers Anatomy of the Frog. Engl. Ed.) rests by a broad base on the cell. The opposite broader endof the cell usually appears rounded, but sometimes a finefibril may be seen springing from it, and this probablybecomes continuous with a terminal fibril of the auditorynerve though the connection has not been actually characters of taste-cells may be learned by an inspectionof fig. 15, ^. Digitized by Microsoft® go COMPARATIVE ANATOMY It should be noticed that epitheHa play a very importantpart in the economy of the animal, and that the cells of the
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