THE EPIBRANCHIAL ORGAN, ITS INNERVATION AND ITS PROBABLE FUNCTIONING IN HETEROTIS-NILOTICUS (PISCES, TELEOSTEI, OSTEOGLOSSIDAE)

The high level of encephalization in Heterotis niloticus is due, in part, to a voluminous lobus vagalis, which has the form of a cauliflower and receives the fibers of a strong branch of the 10th (vagal) nerve. This vagal branch comes from a special branchial apparatus, the epibranchial organ, considered to be an air-breathing organ by some, and a microphagous apparatus by others. This organ has a spiral, snail-like form and its lumen is a blind-alley. Its study in a juvenile fish 10 cm SL shows that it has two canals: a peripheric one for water entrance and a central one for food exit. The epithelium between these two canals contains numerous gustatory buds, the innervation of which constitutes the branch of the vagal nerve. This epithelium is also very rich in mucous cells, which probably correspond to a muco-microphagous feeding apparatus. The exit canal, which receives the mucous string enriched with food particles, enters directly into the oesophagus. Striated muscles, attaching along the spiral tours of the epibranchial organ, probably serve as the motor that pumps water in and out and supplies the classical ciliary apparatus of the mucophagous feeding organs.