On the one hand, amphioxus has the basic characteristics of chordates, such as spinal cord, dorsal neural tube and branchial fissure, on the other hand, it is different from vertebrates, and its body structure has a series of primitive characteristics, such as headless and brainless, no appendages, no heart and primitive segmented muscles. Therefore, from the perspective of comparative anatomy, amphioxus is a transitional type between invertebrates and vertebrates. It is an indispensable and precious specimen for studying animal evolution. Darwin commented on the work of Russian embryologist Ke Valevski in discovering the status of amphioxus, saying, "This is the greatest discovery, which provides the key to reveal the origin of vertebrates".