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Metamorphosis of the primitive Agnathan vertebrates, the sea lampreys, Petromyzon marinus L., is a programmed and highly synchronized sequence of changes in external and internal structures. Before metamorphosis, the olfactory organ is relatively small and contains thin densely packed cells, whereas after metamorphosis, it is large, and contains lamellar folds with wider more distinct olfactory epithelial cells (VanDenbossche et al., '93). We have used scanning electron microscopy and right microscopy of 1 $\mu$m sections of epoxy embedded tissue to document changes in the structure of the olfactory sac during the seven stages of metamorphosis (M1-M7). The changes I observed in the olfactory organ (nasal sac) of landlocked sea lampreys can best be described as a systematic process of growth (M1 and M2), followed by remodeling (M3 to M5) and expansion of the transformed structure (M6 and M7). The specific changes during metamorphosis are: (1) doubling of the wet weight of the nasal sac; (2) at M3, olfactory lamellae of the olfactory organ and germinal areas in trough-like depressions between olfactory lamellae, commence development; (3) at M3 nonmyelinated nerve fascicles start to increase in size and diameter; (4) at M4, the nasal valve that separates the nasal tube from the olfactory organ starts to form; (5) the nasal septum transforms from a small partial fold of epithelium to a larger, more encompassing and complete lamellar fold with olfactory epithelium; (6) a transitional thickening of the olfactory epithelium occurs (in ammocoetes, M3-M5 and post metamorphic (PM) specimens, the average thickness was 73, 93 and 64 $\mu$m respectively); and (7) diverticula of the accessory olfactory organ invade the olfactory mucosa in M4, and are prominent in M7 and PM animals. Overall, olfactory organ transformation includes structural reorganization and the addition of structures between M3 and M5. Growth and maturation of these transformed and newly developed structures continues through M6 and M7. The pattern of change seen in the olfactory organ (nasal sac) most resembled changes seen in the endostyle and liver. In all these organ systems, the most dramatic or significant changes occurred between M3 and M5.Dept. of Biological Sciences. Paper copy at Leddy Library: Theses & Major Papers - Basement, West Bldg. / Call Number: Thesis1993 .V36. Source: Masters Abstracts International, Volume: 32-06, page: 1597. Thesis (M.Sc.)--University of Windsor (Canada), 1993.
VanDenbossche, Jamie., "The olfactory organ of sea lamprey, Petromyzon marinus L. during metamorphosis: Morphological changes and morphometric analysis." (1993). Electronic Theses and Dissertations. 4129.