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The ultrastructure of the funnel-like tubes of the olfactory organ in Rhinomuraena ambonensis was investigated by electron microscopy. Frontal sections of the tubes demonstrate a symmetrical arrangement of an inner epithelium, connective tissue, and an outer epithelium. The surface of each peripheral cell of the epithelia bears a system of small ridges which does not correspond with that of the adjacent cells. In case of a rectilinear course of the epithelial cell borders, numerous desmosomes are located along the cell membranes. The fine structure of the desmosomes was analysed. Number and size of the intercellular spaces increases with increasing depth of the epithelium cell layers. The fine structure of epithelial, basal and secretory cells is described. The outer region of each epithelial cell contains densely packed tonofilaments. The fine structure of sensory “buds” which are sparsely distributed within the outer epithelium of the funnels is described. The basal border of the epithelia consists of a rather thick basal membrane. Blood vessels, nerve bundles, chromatophores and storage cells with cristalline inclusions are embedded in the connective tissue. The fine structure of the chromatophores and storage cells is described. The importance of desmosomes, tonofilaments and intercellular spaces, as well as the basal membrane and the amount of collagen is discussed in relation to the reinforcement of the funnels.

In three individuals of the moray eelRhinomuraena ambonensis (Barbour), the functional morphology and histology of the olfactory organ as well as the histology of the different head appendages were investigated. The edges of the anterior nares are extremely extended, forming a funnel-like wide opening through which the odour water passes. Even when the fish does not move, an effective ventilation of the olfactory chambers is maintained by a permanent water current towards the funnel opening induced by the peristaltic movements of the musculature of the gill chamber (principle ofBernoulli). The histological structure of the head appendages (funnels, rostrum and mandibulary barbels, which are all skin projections) is described. The epithelia of all these appendages bear sensory organs which are similar to taste buds. The two olfactory organs are of extremely large size. Each chamber contains about 100 olfactory lamellae which are arranged in two lines (90°-type;Holl 1965). A cylindrical cavity extends between the inner edges of the olfactory lamellae through which the water runs to the posterior nare. Interlamellar microventilation is produced by numerous turbulences which are caused by the edges of the olfactory lamellae and by the kinocilia of the olfactory epithelium. The histological structure of the olfactory epithelium is similar to that ofAnguilla anguilla. The different results demonstrate thatRhinomuraena ambonensis is probably a macrosmatic fish.

The paper deals with the structure of the olfactory organ, its accessory parts and the forebrain in the deep-sea fishAphanopus carbo. On each side of the head only one opening leads to the olfactory chamber. The olfactory folds are arranged in a rosette-like pattern, resembling the 360°-type. Secondary folds on the main folds may serve as an enlargement of the surface of the olfactory epithelium. Most of the surface area of the olfactory folds is covered by the olfactory epithelium, indicating that the receptive area is of optimal extension. The histological structure of the olfactory epithelium is similar to that in other teleost species. The number of olfactory receptors amounts to about 5×106 to 107 for the single organ. Numerous secretory cells of unknown function are located within the olfactory epithelium. The olfactory chamber is enlarged by three accessory sacs: Two ethmoidal sacs and one lacrymal sac (consisting of two parts). These sacs serve as ventilation aparatus which causes a permanent water current within the olfactory chamber and between the olfactory folds. The action of the accessory sacs is induced by the splanchnokinetic. The forebrain ofAphanopus carbo is well developed; its size ranges between that of forebrains in microsmatic and macrosmatic teleost species. A detailed investigation of the forebrain is in preparation. The diagnosis of the different parts of the olfactory apparatus ofAphanopus carbo demonstrates clearly that — in addition to the eye — this sense organ is well developed (relative to that in other teleosts). This fact suggests thatAphanopus carbo is related to a group of teleost species characterized by optical and olfactory orientation mechanisms of high performance.