The biologists noticed that once each day the colour of the fiddler crab is especially dark, and that each day this happens fifty minutes later than on the day before.

• 生物学家注意到，招潮蟹的外壳每天都会有颜色特别黑的时刻，而这种颜色的变化每过一天就会推迟50分钟出现。