Comparison of gastrulation and early neurulation stages between the turtle and the chick.

Stage correspondances at turtle stage 0 to 2 were mainly based on Otx2 expression pattern, which appears highly dynamic and very similar in the turtle and in the chick (see Dicussion). Additional morphological criteria were used at turtle stages 2 and 3, respectively characterized by the presence of the notochord in its anterior-most parts (head process : stage HH5 in the chick and 2 in the turtle), and the elevation of the anterior neural folds (head fold : stage HH6 in the chick and 3 in the turtle).

龟类0至2期的分期对应关系主要基于Otx2的表达模式，该模式在龟类与鸡胚中呈现高度动态且极为相似（详见讨论部分）。龟类2期和3期则额外采用形态学判定标准：二者分别以脊索（notochord）存在于其最前端区域（头突（head process）：鸡胚对应HH5期，龟类对应2期）以及前神经褶（anterior neural folds）隆起（头褶（head fold）：鸡胚对应HH6期，龟类对应3期）为特征。