世界上的螃蟹,除了一两种特殊的之外,几乎都是横着走路的。这是为什么呢? 人们知道,许多动物是依靠地磁场来判断方向的,特别是对于回游、迁徒性动物来说,地磁场起了很大的作用。但是地磁场不是固定不变的。据古地磁学研究,在地球形成以后的漫长岁月中,地磁南北极 The world’s crabs, except for one or two specialities, are almost horizontally walking. Why is this? People know that many animals rely on the Earth’s magnetic field to determine the direction, and especially for the returning and displacing animals, the magnetic field plays a major role. But the geomagnetic field is not fixed. According to ancient geomagnetic research, in the long years after the earth was formed, the magnetic north and south