The most striking example is a family of small fish living in tropical American waters called the Poeciliidae among whom guppies, mosquito fish and the four-eyed anableps are best known.

The flow of nitrogen from night-soil in rural China is valuable, whereas human excrement in an urban center is a pollution problem.

obsidian:

Now we've sorted that out, the easiest way is up the clough and along the bridleway.