Encyclopedia of Adaptations of the Natural World https://books.google.co.ug/books?id=pWhFELnNZzMC&pg=PA62&lpg=PA62&dq=%E2%80%9Cbeat+in+one+particular+direction,+like+the+pendulum+of+a+clock,%E2%80%9D+says+the+Encyclopedia+of+Adaptations+in+the+Natural+World.&source=bl&ots=EKkO9YEW_V&sig=i6C4rxhdJ4-ZvXkf_#v=onepage&q=%E2%80%9Cbeat%20in%20one%20particular%20direction%2C%20like%20the%20pendulum%20of%20a%20clock%2C%E2%80%9D%20says%20the%20Encyclopedia%20of%20Adaptations%20in%20the%20Natural%20World.&f=false