THE MORPHOLOGY OF THE OLFACTORY EPITHELIUM IN LARVAL, JUVENILE AND UPSTREAM MIGRANT STAGES OF THE SEA LAMPREY, PETROMYZON-MARINUS

The structure of the olfactory epithelium in the larval, juvenile and upstream migrant stages of the sea lamprey, Petromyzon marinus, was in vestigated by light microscopy and by scanning and transmission electr on microscopy. Ciliated olfactory receptor cells (ORC) were present in all stages. In larval specimens, the number of ORC was 20+/-8 ORC per 100 mu m length of olfactory epithelial surface. In juveniles and in upstream migrants the ORC density dropped to 9+/-2 and 6+/-2 ORC/100 m u m, respectively. Sustentacular cells were microvillar in the smalles t larval stage (with a body length of 15 mm) and ciliated in larger la rvae and later life stages. The morphological characteristics of the o lfactory mucosa suggest that the sea lamprey's capacity for use of the olfactory system extends into the larval stage, and that there are sp ecific changes associated with metamorphosis.