DEVELOPMENT OF THE CILIATURE PATTERN ON THE EMBRYO OF THE SQUIDLOLIGO PEALEI:A SCANNING ELECTRON MICROSCOPE STUDY

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Abstract
Four different types of beating ciliated cells appear at different times during development of the squid embryo. Ciliated cells of the external yolk sac appear 1st as polygonal flattened cells. The cilia are uniform in diameter and end in a blunt or slightly tapered tip. The beat is asynchronous, uncoordinated and unidirectional toward the vegetal pole. In later development these cilia develop a flattened paddle at or near their tips, apparently associated with coiling of the axonemes within them. Paddle-type ciliated cells develop on the embryonic body. They are always isolated from each other. Their beat is unidirectional and asynchronous. The axis of the paddle is parallel to the cell surface on the return stroke and is perpendicular on the power stroke. There is little resistance on the return stroke, but the effectiveness of the power stroke is increased. Paddle-type ciliated cells appear on the mantle and head in patches. A 3rd type of ciliated cell appears in rows on the mantle. These cilia beat in synchronized metachronic waves and are called uniform-type ciliated cells. The 4th type of ciliated cells, the single-file type, appears on the head and ventral arms of the late stage 28 embryo. They beat in a synchronized side to side wave. At hatching the mantle epithelium degenerates and is sloughed off. Presumably the epithelium of the head is also lost. The function of the 1st 3 ciliated cell types is discussed.