Objective To study species and distribution of fleas in Zhangjiakou.

摘要目的研究张家口市蚤的种类及其分布.

Like the taxonomists before him, Darwin could study species only with the naked eye, observing the color of a bird's feathers or counting the plates on a barnacle.

达尔文就像在他之前的分类学家，只能用肉眼研究物种，观察鸟羽的颜色，或是计算藤壶片壳的数量。