There are 5 stages during the development of embryo, including the stage of 2-celled proembryo, multicellular proembryo, globular proembryo, pyriform proembryo, differential embryo and mature embryo.

胎发育经过二胞、多胞、球、梨、分化和成熟阶段。

We also describe the basic principle of white dwarf cosmochronology and its application in defining the age of the Galactic disk, globular clusters, open clusters and Galactic halo.

介绍了白矮宇宙纪年学研究的基本理及其在银盘、球状团、疏散团以及银晕年龄确定方面的应用现状。