Studies On The Structure And The Development Of Olfactory And Visual Organ In The Southern Catfish(Silurus Meridionalis Chen)

The structure and the development of olfactory organ and visual organ in Silurus meridionalis were studied by means of the light microscope, scanning and transmission electron microscope between March,2000 and March,2001.The result is indicated as following:The olfactory lamella of the southern catfish is well-developed and is composed of two layers of epithlium enclosing a thin stromal sheet.the pattern of the arrangemnt of the olfactory lamella may be classified as type G The distribution of sensory epithelium and indifferent epithelium on the olfactory lamella is classified as type I . The sensory epithlium,which is composed of receptor celK ciliated non-sensory celK supporting celK mucous cell and basal cell, is continuous except for the margin of the lamella where the indifferent epithlium is distributed. The densely-distributed cilias exist in sensory areas through scanning electron microscope and Secretory vesicle in the whole surface of olfactory lamella. The surface of indifferent areas is smooth, occasionally where a cluster of cilia is distributed. All types of the cells in olfactory epithlium have cell organs which the common cells possess through transmission electron microscope. A lot of oval mitochondrias and vesicles exist in the sensory cell. Mucous cells are full filled with the mucus particles. Silurus meridionalis have a strong olfactory ability and is a typical nose fish.The eye in Silurus meridionalis is comparatively small and not enough well-developed, the structure of which is similar to that of other teleosts. Silver film exists in the choroids. The retina of Silurus meridionalis is made up of ten layers and its average thickness is 670um. there are three kinds of photoreceptors in the retina: rods, single cones and double cones. The number of ganglion cells which are arranged sparsely in ganglion layer is comparatively few and have 2-3 ganglion cells per 100um in ganglion layer. Each ganglion cell receives about 3 bipolar cells,and each bipolar cell receives about 4 photoreceptors. That is to say each ganglion cell has a smaller receptive field. The ratio of thickness ofphotoreceptor layer to photo-transfering layer is about 3:2 and the ratio of the number of photo-recepted cells to ganglion cells is about 12:1.That indicates structural trait of the retina that photo-recepted cells flock together to ganglion cells in moonlighting animals.There is the genesis of olfactory organ 23h after fertilization at water temperature 21 ?0.5℃. The olfactory plate is formed by the thickening of the neural epidermis on the lateral side to the prosencephalon rudiment in the vesicle stage of the embryo. Olfactory plate concave slightly from the dorsal side of anterior head at hatching to form olfactory pit. The olfactory epithelium start to differentiate after hatching day 2; The first lamellae is present in the posterior end of olfactory chamber and anterior and posterior nostril have formed after hatching day 7. The first four lamellae after day 10. The development of basic histological structure of olfactory organ is comparatively perfect at day 40. After this, the number of olfactory lamellae continually increases and the area of olfactory epithelium unremittingly enlarges. Olfactory lamellaes are formed owing to the upheaval of olfactory epithelium from posterior to anterior, as a result, the development of lamellae in the posterior end of olfactory chamber is the earlier than those in the anterior and middle and the surface of that is the biggest.The development of visual organ is the earliest among the sensory organs. The differentiation of the retina is the earliest among the visual organs. Optic cup is made up of neuroepithelium layer and pigment epithelium layer at hatching. 12h after hatching, there are some pigments on the outer optic cup; 2d after hatching, the cell in the inner start to differentiate into ganglion layer, outer nuclear layer and inner nuclear layer. There are a small quantity of cones in the retina. With 62h after hatching, visual nerve elementarily for...