试论脊椎动物的进化

A Tentative Discussion on the Evolution of Vertebrates

生物的进化 ,同时经历两个途径 ,一是由低级向高级进化 ,二是由水生向陆生进化。生活在大陆上的脊椎动物 ,是由生活在海洋中的脊椎动物 ,登上大陆后 ,分别进化为两栖类、爬行类、鸟类和哺乳类动物。

The are two ways for animals' evolution. One is from lwer level to higher level, the other is from aquatic arimals to terrestrial animals. The vertebrates living or the land can be dated back to the verrebrates living in the ocean, only the evolutio has wndergone four preiods:amphibious animals, reptiles, birds and mammals.