THE SHAPING OF THE ORNAMENTED FERTILIZATION MEMBRANE OFCOMANTHUS JAPONICA(ECHINODERMATA: CRINOIDEA)

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Abstract
1. This is the first electron microscopic description of fertilization membrane formation in a crinoid echinoderm. 2. The fertilization membrane is a composite structure consisting of a thin vitelline coat plus a thick layer of material originating from the cortical granules. 3. The fertilization membrane elevates from the plasma membrane, leaving a perivitelline space several microns wide; no trace of a hyaline layer appears in this space. 4. By 2 min after the start of cortical granule exocytosis, ridges about 15 µ high are erected on the surface of the fertilization membrane. The ridge pattern is determined by the egg jelly which is divided into several hundred clumps on the egg surface; each jelly clump apparently acts as a physical restraint on the fertilization membrane surface immediately beneath, and ridges can rise only between the jelly clumps. 5. The morphogenetic role of the egg jelly is corroborated by observations on living eggs; a ridgeless fertilization membrane can be produced if the jelly is first removed from the egg surface.