The distribution of the olfactory tracts in the bullhead catfish, Ictalurus nebulosus.

Using degeneration staining methods, central projections of the olfactory tracts in the bullhead catfish, Ictalurus nebulosus were studied. Seporate lesions were made of the lateral and medial olfactory tracts in an attempt to separate their zones of projection. Three major terminal fields were found: lateral, medial and central-posterior complex. Two additional minor projections were seen: interbulbar and hypothalamic. The lateral division of the olfactory tract terminates in lateral, central and hypothalamic terminal fields. The medial tract projects to lateral, meedial, posterior and hypothalamic fields. All terminal fields were found bilaterally; the lateral tract partly crossing in both the anterior commissure. A small intellbulbar commissure was also found to contain medial tract fibers. Evidence is given to show that the anterior olfactory nucleus, if present in catfish, may be located within the olfactory bulb itself. Similarities between mammalian and teleost olfactory systems are also discussed.