中国对虾幼体期视觉器官的发育

DEVELOPMENT OF OCULAR ORGANS IN THE LARVAL STAGES OF PENEUS CHINENSIS

于1994年3—5月，以中国对虾无节幼体6个业期（N1－N6）、蚤状幼体3个亚期（Z1．－Z3）、糠虾幼体3个亚朋（M1－M3）及仔虾（P）各时期的幼体为材料，用日产Olympus万能研究显微镜观察研究各期幼体单限及复眼的发育。结果表明：在中国对虾无节幼体N1－N66个亚期，单眼的两侧均有复眼的原基组织。在Z1期，复眼原基发育为眼叶，其表层眼基细胞与内层神经组织分离。Z1后期，眼叶表层服基细胞发育成众多放射状原始小眼单位。Z2期，眼叶表层与内层分别发育为复眼和眼柄；原始小眼单位分化为小眼。每个小眼表面有4个角膜生成细胞，它们向上二分泌形成圆形角膜；角膜生成细胞卜面为4个拉长的锥体细胞，其用围散布着虹膜色素细胞；锥体细胞卜面的小网膜细胞呈杆状，其截向内未见视杆形成；Z2，后期，晶锥发生于锥体细胞底部。Z3期，视杆已形成，晶锥向上肝增大。单限一直存在。M1期，复服内各小眼分化由远体轴侧向近体轴侧继续进行；单眼升始退化，仅见色素及其两侧退化的单晶眼的痕迹。M2，M3期，各小眼继续发育。单限仅残存色素。仔虾期，单眼彻底消失，复眼内各小眼的发育基本完成。

The samples including Nauplium (N1-N6), Zoea (Z1-Z3), Mysis (M1-M3), and Postlarvae of the shrimp (Penaeus chinensis) were collected from artficial nursing ponds of the shrimp every two days during March-May in 1994, fixed in neutraI formalin, Bouin's and Carnoy's liquids. Parafin sections of 5- 7μm in thickness were prepared. Histological studies on the development of the ocular organs in the shrimp were carried out with an Olympus research microscope. The results show that in the Naupia (N1-N6), there are two blocks of rudimental tissues of the compound eyes (RTC) locating bilaterially on two sides of the simple eye. At the Z1 stage, RTC develops to become ocular lobes (OC) consisting of two layers-the surface layer is the photoreceptive rudiment and the deeper one is the neuropil region.The cells on the suribee of OC proliferate and elongate to form several clustels arranging radially, these are proto-xommatidial units. At the Z2 stage, the compound eyes and eyestalks occur, and the three ganglia apear in the eyestalk. in the developing ommatidium, the corcea secreted upwards by Ibur coneagen cells lies on the surface of the ommatidium. Four elongated crystalline cone cells are beneath the coneagen cells and surounded by ins pigment cells. The retinular cells are evident in the lower region of the ommatidium. At this stage, the rhabdom has not been formed yet. At the later Z2 stage, the crystalline cone ocurs at the botom of the cone cells. Two senes of pigments- iris and retina pigments separate one ommatidium from another. At the Z3 stage, the rhabdom is produced by the retinular cells. The cone enlarges upwards, but the cone cells become smaller and adhere to the cone. The simple eye is present at Zoea stages and begins to degenerate at the M. stage, but only the trace of the omental cells and the pigment of the simple eye can be seen.The omrnatidial diferentiation is not synchronous in the whole compound eye, it initiates in the distal region. Then it progrcsses gradually to the proximal region along the body axis. Dunng M, and M, stages, only the pigrnent of the nauplar eye remalins.At the Postlarval stage, the sirnple eye disappears tholxiughly and ommatidial formation in all regions of the compound eye is accompolished.