我们平时去一个不熟悉的地方，常常需要手机导航帮忙。可是自然界中有些生物，却像是天生就自带指南针属性，可以长途跋涉不迷路，例如帝王蝶、鲑鱼、龙虾、海龟、迁徙的鸟类等。还有一些生物，会按照地球磁场的方向筑巢、打洞或者睡眠，如指南白蚁、裸鼹鼠等。科学家们认为，生物之所以具有这种神奇的“方向感”，原因之一在于它们的感觉系统除了视觉、听觉、嗅觉、触觉、味觉之外，还有被称为“第六感”的磁觉，即生物利用地磁场准确寻找正确的方向。
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