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

Abstract

1. Four types of beating ciliated cells, which appear at different times during embryonic development of the squid Loligo pealei, are described.2. The ciliated cells of the external yolk sac first appear during or at onset of organogenesis, as polygonal flattened cells in a pavement-like arrangement. The cilia of these cells are uniform in diameter and end in a blunt or slightly tapered tip. Their beat is asynchronous and uncoordinated, but unidirectional toward the vegetal pole. A large hemal space develops between these cells and the yolk syncytium of the external yolk sac. In later stages of development, when primary respiratory function is assumed by the gills (and probably the skin), the cilia on those cells develop a flattened paddle at or near their tips, which apparently is associated with coiling of the axonemes within them.3. Paddle-type ciliated cells develop on the embryonic body proper and are always isolated from each other except at the anterior edges of the mantle. These cilia beat unidirectionally and asynchronously. The axis of the paddle is parallel to the cell surface on the return stroke, thus offering little resistance to the bending of the cilia, and is perpendicular to the direction of the power stroke, thereby increasing the effectiveness of the power stroke. Cells of this type appear on the mantle and head in patches, but not in areas to be covered by other tissues such as the mantle.4. At or just before Stage 26, a third type of ciliated cell appears in rows on the mantle. The individual cilia are uniform in diameter and end in a tapered tip. The cilia on these cells beat in a metachronic wave synchronized among several cells aligned in rows. These lines of "uniform-type" ciliated cells are apparently very effective because the embryos begin to swim and tumble actively in the chorionic fluid and circulate it rapidly. This probably enhances respiration and prevents the embryo from sticking to the inner surface of the chorion.5. A fourth type of beating ciliated cell, the "single-file" ciliated cell, appears on the head and ventral arms of the late Stage 28 or early Stage 29 embryo. The cilia of these cells are aligned in single file on the anterior-posterior axis and beat in a synchronized side-to-side wave. The function of these cells is unknown. 6. At hatching, the entire mantle epithelium degenerates and is sloughed off.Presumably, the epithelium of the head is also shed, but was unobserved by us.