Fernández J, Stent G S
J Embryol Exp Morphol. 1982 Dec;72:71-96.
The germinal plate of 5- to 12-day-old embryos of the leech Hirudo medicinalis consists of an anterior and a posterior sector that differ both structurally and developmentally. The posterior sector includes the five pairs of teloblasts and five paired longitudinal bandlets of stem cells and their descendant blast cells. The mesoteloblast pair and their descendant cells of the m bandlet divide spirally and give rise to bilaterally paired cell clusters. The four ectoteloblast pairs and their descendant cells of the n, o, p and q bandlet pairs divide unidirectionally and give rise to paired one-cell-thick and four-cell-wide ectodermal arches. The developmentally more advanced anterior sector of the germinal plate consists of differentiating ectodermal and mesodermal cells engaged in organogenesis. The mesodermal cell clusters develop into somites, whereas the expanding ectodermal arches develop into nerve cord ganglia and epidermis. Rostrocaudal expansion of somite tissue results in the formation of obliquely oriented intersegmental septa, causing the ganglia to take on an intersegmental distribution. The first sign that formation of body segments has been completed is the appearance of a bilateral gap in the mesodermal bandlet of the posterior sector of the germinal plate. This gap seems to trigger degeneration of the posterior sector of the germinal plate.
医用水蛭5至12日龄胚胎的生发板由前区和后区组成，这两个区域在结构和发育上均存在差异。后区包括五对端细胞和五对干细胞及其后代胚细胞的纵向带。中胚层端细胞对及其m带的后代细胞呈螺旋状分裂，产生双侧成对的细胞簇。四对外胚层端细胞对及其n、o、p和q带对的后代细胞单向分裂，产生成对的单细胞厚、四细胞宽的外胚层弓。生发板发育更成熟的前区由参与器官发生的分化外胚层和中胚层细胞组成。中胚层细胞簇发育成体节，而不断扩展的外胚层弓发育成神经索神经节和表皮。体节组织的头尾向扩展导致斜向的节间隔膜形成，使神经节呈节间分布。生发板后区中胚层带出现双侧间隙是体节形成完成的首个迹象。这个间隙似乎触发了生发板后区的退化。
