【英语时差8,16】蚯蚓（上）

（单词翻译）

 Charles Darwin is best known for his studies of evolution by means of natural and sexual selection, but did you know he was also a pioneer in the study of earthworms? After watching an earthworm s-l-o-w-l-y drag a leaf into its burrow¹, Darwin became fascinated by these unassuming creatures. He began an exhaustive study of worm behavior, sensory² abilities and digestion³. His book on worms was the first to describe the enormous impact of earthworms on our lives. Darwin noticed that a thick layer of charcoal⁴ and cinders⁵ that he’d spread across a large field two years earlier was now uniformly covered by several inches of earth. He surmised⁶ that what appeared to be the “sinking” of the charcoal layer was actually the result of earthworm “castings.” Earthworms swallow soil, extract nutrients⁷ from it, then excrete the rest up onto the surface. These excretions—small dark mounds⁸ of fine dirt you may see dotting the ground—are called castings.