THE ULTRASTRUCTURE OF THE SKIN OF NEOPHOCAENA PHOCAENOIDES AND COMPARISON WITH OTHER CETACEANS

Although the ultrastructure of the skin of Neophocaena is similar to that of marine odontocetes, some features are worthy of notice. Numerous membrane coating granules lie close to plasme membranes of the superficilal cell layers. These granules have good function to protect the hydrotropic substances to discharge from inside of the skin into external environment. Most probably, this structure is advantageous to dolphin moving from sea water to freshwater of Changjiang River. A lot of tonofilaments are present in the strata of the skin. They can strengthen the connexion among the cells which are faced with strong pressure and rub on the skin due to diving and fast swimming. Numerous single and clustered encapsulated nerve endings lie at the bases of the sturdier dermal papillae in the region of the tubercles. Many groups of similar encapsulated nerve endings are present in the dermal ridge of the lower jaw. A lot of bundles of myelinated nerve fibres are present in the dermis and the hypodermis of the jaw and the tubercles. These integumental features can be correlated with some of the behavioural characteristics exhibited by Neophocaena in the river, for instance, carrying their calves on their backs and seeking the food from the bottom of the water.