The Merkel Cell in the Labial Ridge Epidermis of the Anuran Tadpole

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Abstract
The appearance and cytodifferentiation of the Merkel cell were studied by EM using the developing labial ridges of Rana japonica. The most primitive Merkel cell was identified with specific cored granules with an average diameter of .apprx. 90 nm. Such a primitive Merkel cell was found in the basal layer of the primitive labial ridge epithelium. As the primitive labial ridge continued to mature, the primitive Merkel cell accumulated on increased number of the specific granules, developed digital shaped cytoplasmic processes and came into contact with nerve fibers. When the labial ridge was sufficiently developed, the cell showed typical morphological features of the mature Merkel cell except for a small accumulation of tonofilament-like structures and glycogen particles. The position of the Merkel cell in the epithelium changed from the basal layer to the 3rd basal layer during development. It was difficult to find the Merkel cell in the mesenchymal layer of the developing labial ridges. The cytodifferentiation of the Merkel cell in the labial ridge of an anuran tadpole may occur within the epithelium.