《太平广记·卷四百零六·草木一（》
外边有一层粗皮，就像大腹皮。粗皮下是一层硬壳，光圆而坚硬，二三分厚。
外有粗皮，如大腹子；次有硬壳，圆而且坚，厚二三分。
There is a layer of coarse skin outside, like a big belly skin. Under the coarse skin is a hard shell, smooth and hard, two or three tenths thick.