The Morphology of the Organum Olfactus of a 32 mm Embryo of the Brachiopterygian Fish Polypterus senegalus

Abstract

Anatomically the brachiopterygian organum olfactus is unique among craniates. As revealed by the present study of Polypterus senegalus, it consists of an incurrent and an excurrent tube, a body and six lobes. Luminally these divisions are extensively covered with cilia, the actions of which cause water to flow through the organ. The proximal extremities of the two tubes communicate directly with one another, allowing water to bypass the body and the lobes. The body is subdivided by means of seven infolds into a central part and two peripheral parts. Of these, the central part directs water to the lobes; the peripheral parts drain the lobes and lead water to the excurrent tube. Each lobe has an axial portion and two rows of alternating lobuli. Interlobularly infolds of the axial portion subdivide the lobar lumen in such a way that movement of water is possible. Olfactory neurosensory cells occur in the rear of the incurrent tube, as well as in the lobes. Probably the degree of stimulation of the tubal receptors determines whether the water taken in is to bypass the lobes.

Development of the Snout of the Australian Lungfish Neoceratodus forsteri (Krefft, 1870), with Special Reference to Cranial Nerves

“…It is well separated from the olfactory epithelium and is always lodged in the posteromesial wall of the anterior nasal tube. It might be comparable with similarly shaped patches of olfactory epithelium described by Bjerring (1988) as vigiles olfactoriae of the anterior nasal tube in Polypterus (Fig. 5A).…”

Early Ontogeny of the Olfactory Organ in a Basal Actinopterygian Fish: <i>Polypterus</i>

“…and Erpetoichthys (syn Calamoichthys calabaricus ) are large and have a complicated structure, unique among fish [Pfeiffer, 1968; Theisen, 1970; Schulte and Holl, 1971; Bjerring, 1988; Zeiske et al, 1992]. The olfactory epithelium consists of basal cells, supporting cells, olfactory receptor neurons (ORNs) and ciliated non-sensory cells [Schulte and Holl, 1971].…”

“…A few studies are available concerning the gross morphology of the adult condition [Pfeiffer, 1968, 1969; Theisen, 1970], the detailed anatomy of a larval nasal sac [Bjerring, 1988] in Polypterus , and the ultrastructure of the adult olfactory epithelium in Erpetoichthys calabaricus [Schulte and Holl, 1971]. Some remarks on the early development of the olfactory placode are mentioned in the ontogenetic and microscopical study of [Kerr, 1907] based on Budgett’s work [Budgett, 1902] and material collected at the Gambia River.…”