EYE MORPHOGENESIS IN THE GOBIOCYPRIS RARUS

Gobiocypris rarus was a new genus of danioninae from China. It had some good characteristic such as strong vitality,short mature period and breeding every yearwhen raised in the Lab. So recently it was reguarded as an ideal experimentalmaterial. Eye morphogenesis in the Gobiocypris rarus was observed and described in detail. Retina, lens and cornea development wereour emphases. Meanwhile, thethickness of the pigment epithelium layer and the neural retina from Neurula period to Tail vesicleperiod and the total thickness of the retina from Caudal fin period to Hatching period of Gobiocypris rarus were measured.The results indicated that the eye morphogenesis in the Gobiocypris rarus begins with the formation of optic primordia. Un -like amphibians and mammals, the optic primordia are the evaginations from the forebrain as solid masses of cells.They werecommunicate with the neural keel and the elliptic cells within the primordium are radially arranged. In this period mesenchymecells are also observed ventral to the optic primordium. The optic primordia bend ventrally and elongate laterally and take on adistinctive wing -like shape in tail bud period. They had contacted with the ectoderm closely already. In tail vesicle period, theoptic cup is well formed. The out layer of theoptic primordia clings to the ectodermwill give rise to the neural retina whereas theother part of theopticprimordiawill give riseto the pigment epithelium. The neural retina will not differentiate until mitosis with -in the pigment epithelium layer stopped and pigment was synthesized after the Tail vesicle period. The orderly differentiation ofthe two layer of retina is probably related to thespace in embryo and the mesenchyme nearby. FromNeurula period to Tail vesicleperiod, the thickness of the pigment epithelium layer reduced evidently from 42.3±0.8μm to 4.8±0.4μm while the thicknessof neural retina increased indistinctively from 37.1±0.2μm to 43.7±0.6μm. From Caudal fin period to Hatching period, thetotal thickness of the retina increased gradually from 42.7±1.2μm to 98.3±2.1μm.Retinal differentiation in the Gobiocypris rarus generally follows the direction inner-to-outer sequence characteristic of allvertebrate species. It commenceswith the differentiation of the inner layer of the bottom of the optic cup and then to the peripheryand the outer layer.Lens, cornea and other adnexa are basically formed before hatching.