Lampreys, which represent the oldest group of living vertebrates (cyclostomes), show unique eye development. The lamprey larva has only eyespot‐like immature eyes beneath a non‐transparent skin, whereas after metamorphosis, the adult has well‐developed image‐forming camera eyes. To establish a functional visual system, well‐organised visual centres as well as motor components (e.g. trunk muscles for locomotion) and interactions between them are needed. Here we review the available knowledge concerning the structure, function and development of the different parts of the lamprey visual system. The lamprey exhibits stepwise development of the visual system during its life cycle. In prolarvae and early larvae, the ‘primary’ retina does not have horizontal and amacrine cells, but does have photoreceptors, bipolar cells and ganglion cells. At this stage, the optic nerve projects mostly to the pretectum, where the dendrites of neurons in the nucleus of the medial longitudinal fasciculus (nMLF) appear to receive direct visual information and send motor outputs to the neck and trunk muscles. This simple neural circuit may generate negative phototaxis. Through the larval period, the lateral region of the retina grows again to form the ‘secondary’ retina and the topographic retinotectal projection of the optic nerve is formed, and at the same time, the extra‐ocular muscles progressively develop. During metamorphosis, horizontal and amacrine cells differentiate for the first time, and the optic tectum expands and becomes laminated. The adult lamprey then has a sophisticated visual system for image‐forming and visual decision‐making. In the adult lamprey, the thalamic pathway (retina–thalamus–cortex/pallium) also transmits visual stimuli. Because the primary, simple light‐detecting circuit in larval lamprey shares functional and developmental similarities with that of protochordates (amphioxus and tunicates), the visual development of the lamprey provides information regarding the evolutionary transition of the vertebrate visual system from the protochordate‐type to the vertebrate‐type.

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七鳃鳗视觉系统的逐步发展及其进化意义

七鳃鳗，代表最古老的活脊椎动物群（圆口纲），显示出独特的眼睛发育。七鳃鳗幼虫在不透明的皮肤下只有像眼斑一样的未成熟眼睛，而在变态后，成虫具有发育良好的成像相机眼睛。为了建立功能性视觉系统，需要组织良好的视觉中心以及运动部件（例如用于运动的躯干肌肉）以及它们之间的相互作用。在这里，我们回顾了有关七鳃鳗视觉系统不同部分的结构、功能和发展的可用知识。七鳃鳗在其生命周期中表现出视觉系统的逐步发展。在前幼虫和早期幼虫中，“初级”视网膜没有水平细胞和无长突细胞，但有光感受器、双极细胞和神经节细胞。在这个阶段，视神经主要投射到前顶盖，内侧纵束 (nMLF) 核中的神经元树突似乎接收直接视觉信息并将运动输出发送到颈部和躯干肌肉。这个简单的神经回路可能会产生负趋光性。在幼虫期，视网膜的外侧区域再次生长形成“次级”视网膜，形成视神经的地形视网膜保护，同时眼外肌逐渐发育。在变态过程中，水平细胞和无长突细胞首次分化，视顶盖扩大并变成层状。成年七鳃鳗拥有复杂的视觉系统，用于图像形成和视觉决策。在成年七鳃鳗中，丘脑通路（视网膜-丘脑-皮质/大脑皮层）也传递视觉刺激。由于七鳃鳗幼虫的主要、简单的光探测回路与原脊索动物（两栖类和被囊类动物）具有功能和发育相似性，因此七鳃鳗的视觉发育提供了有关脊椎动物视觉系统从原脊索动物类型到进化转变的信息。脊椎动物型。