Countless animals, including us, bear external structures without blood supply or nerves - for example, our hair and fingernails, or the scales, claws, and ho rns of other animals.

• 包括人在内的无 数动物都有一些没有血液供应和神经的体外构造，例如，我们的头发和指甲，或者鳞片、爪 子和其它一些动物的角。