15 p. : 24 cm

"Thickenings of the epidermis that project downward and upward, the outward projections of which are surrounded by circular ditches, and that perform a mechanico-sensory function are considered forerunners of hairs (prototriches). Findings of previous observers on such structures in fishes, tailed amphibians, and reptiles are combined with new observations on skin projections of some Salienta to devise a theory of hair and scale evolution. The most primitive prototriches are simple downward thickenings of the epidermis (fishes). In the next stage, a small corium papilla pushes into the epidermal downward thickening and a slight external elevation is added (tailed amphibians). Further phases involve keratinized, sharp, conical projections with circular ditches (coni circumfossati) in spadefoot toads. In some reptiles sensory bristles of similar structure present another phase. The prototriches in tailless amphibians are arranged in characteristic patterns on the warts. Transitional phases between protothrix-studded warts and scale-hair combinations can be shown. The theory is advanced that while the hairs derive from the prototriches, the scales of Amniota derive from warts of amphibians"--P. 14

Title from caption

"March 29, 1957."

Includes bibliographical references (p. 14-15)

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