It has only one pair of eyes, and the other seven pairs of so-called small eyes are gill holes. As early as 1956, after Cheng Peiyi observed the seven-star fish, it was confirmed that the lamprey, described in the biology handout, was the lowest among the six classes (fishes, amphibians, birds, reptiles, mammals, and roundmouth) of the vertebrate subfamily. There are lampreys and blind eels in this class, and no fossils of the class have been found so far. Therefore, the discovery of lamprey is of great value to the study of animal evolution.