Full Idea
Why an orderly system may not be spun from the belly as well as from the brain, it will be difficult … to give a satisfactory reason.
Clarification
He refers to spiders' webs
Gist of Idea
Order may come from an irrational source as well as a rational one
Source
David Hume (Dialogues Concerning Natural Religion [1751], Part 7)
Book Reference
Hume,David: 'Dialogues Concerning Natural Religion' [Penguin], p.91