胚胎:动物出生或孵化前的早期阶段。许多动物的胚胎在发育的早期阶段看起来非常相似。有些特征将继续发育成为肢体、牙齿、或尾巴,有些则会在动物出生之前消失。看出差别一般来说,胚胎的发育是按每一结构的进化顺序进行的。脊骨是所有脊椎动物最先发育的特征结构之一,其一端是头部,另一端是尾。然后四肢的胚芽出现,同时眼睛也会出现。在随后的几个星期,随着有些基因关闭而另一些基因开启,胚胎逐渐变得不同。 Embryo: Animals were born or in early stages before hatching. Many animal embryos look very similar in the early stages of development. Some traits will continue to develop into the body, teeth, or tail, while others will disappear before the animal is born. To see the difference, in general, the development of an embryo takes place in the order of evolution of each structure. The spine is one of the most developed features of all vertebrates. It has a head at one end and a tail at the other end. Then the germs of the limbs appear and the eyes appear. In the following weeks, embryos gradually became different as some genes were turned off and others were turned on.