Youn B W, Keller R E, Malacinski G M
J Embryol Exp Morphol. 1980 Oct;59:223-47.
A scanning electron microscopic, comparative survey of notochord and somite formation including some details of change in cell morphology and arrangement, was made of selected stages of two species of anuran amphibians (Xenopus laevis and Rana pipiens) and two species of urodeles (Ambystoma mexicanum and Pleurodeles waltlii). The ectoderm or neural plate was removed from fixed embryos and the dorsal aspect of the developing notochord and somite mesoderm was photographed. Micrographs of comparable stages of all species were arranged together to form an atlas of notochord and somite formation. Similar morphogenetic events occur in the same sequence in the four species. Notochordal cells become distinguishable from paraxial mesodermal cells by shape, closeness of packing, and arrangement. Notochordal elongation is accompanied by a decrease in cross-sectional area and by cell rearrangement. Somitic mesoderm becomes distinguished from lateral mesoderm by a change in cell shape and orientation, followed by segmentation of somites. The schedule of somite formation was compared and related to the staging series for each species. The urodeles differ from the anurans in that the notochordal region in the early neurula stages in triangular, with the broadest part in the posterior region of the embryo. In anurans it is uniform in width. This difference may reflect differences in gastrulation and in the mechanism of elongation of the posterior part of the embryo in the neurula.
对两种无尾两栖动物（非洲爪蟾和豹蛙）以及两种有尾两栖动物（美西钝口螈和虎纹钝口螈）的特定发育阶段进行了扫描电子显微镜下的比较研究，内容包括脊索和体节形成过程，以及细胞形态和排列变化的一些细节。从固定好的胚胎中移除外胚层或神经板，对发育中的脊索和体节中胚层的背侧进行拍照。将所有物种可比发育阶段的显微照片整理在一起，形成一本脊索和体节形成图谱。这四个物种中相似的形态发生事件按相同顺序发生。脊索细胞通过形状、堆积紧密程度和排列方式与近轴中胚层细胞区分开来。脊索伸长伴随着横截面积减小和细胞重排。体节中胚层通过细胞形状和方向的变化与侧中胚层区分开来，随后体节进行分割。比较了体节形成的时间表，并将其与每个物种的分期系列相关联。有尾两栖动物与无尾两栖动物的不同之处在于，早期神经胚阶段的脊索区域呈三角形，在胚胎后部最宽。在无尾两栖动物中，其宽度是均匀的。这种差异可能反映了原肠胚形成以及神经胚阶段胚胎后部伸长机制的差异。
