. Comparative anatomy. Anatomy, Comparative. Fig. 96.—Developing scales of dogfish, Squalus; sections perpendicular to surface of skin; much enlarged, c, upper layers of epidermis; d, dentine of scale, deposited by dermal cells beneath it; ee, enamel-forming organ of scale—a specialized region of the germinative layer (m) of the epidermis; -p, "pulp", the dentine-forming organ. (From Kingsley.) stratified epithelium such cells are at or near the surface (Fig. 94, u) and open upon it, usually a prolonged and narrow extension of the cell serving as a ductule. The mucus which coats the
. Comparative anatomy. Anatomy, Comparative. Fig. 96.—Developing scales of dogfish, Squalus; sections perpendicular to surface of skin; much enlarged, c, upper layers of epidermis; d, dentine of scale, deposited by dermal cells beneath it; ee, enamel-forming organ of scale—a specialized region of the germinative layer (m) of the epidermis; -p, "pulp", the dentine-forming organ. (From Kingsley.) stratified epithelium such cells are at or near the surface (Fig. 94, u) and open upon it, usually a prolonged and narrow extension of the cell serving as a ductule. The mucus which coats the surface of an earthworm or fish is produced by such unicellular epidermal glands. Many internal epithelia are mucous. (3) A sensory (or neuro-) epi- thelium is one in which certain cells are specialized for reception of stimulation by some agency in the cell's environment. Such a cell is usually elongated and slender and characterized by one or more ex- ceedingly delicate "hairs" or "bristles" at its distal end (Fig. 97). The hair, which is evidently an important part of the receptor mechanism, extends through the cuticula (if present) or is otherwise disposed so as to be readily accessible to the appropriate stimulating agency. Sensory cells may occur in either simple or stratified epithelia. They may be scattered singly throughout an epithelium as in the epidermis of various invertebrates. In the olfactory epithelium of the nasal cavity of mammals the non-nervous cells are of very elongated form and interspersed among them are the even more attenuated olfactory sensory cells ( Fig. 97.—Sensory cells. A, cell from the sense organ (crista acustica) of an ampulla of the ear; B, rod cell from the retina; C, cell from the olfactory epithelium. (From Kingsley, After Fiirbringer.). Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations
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