This collection has the dubious distinction of being one of the most pirated books of all time. Since its first appearance in 1928, illegal editions have appeared with remarkable regularity. The reason? Once considered obscene - it reprints a large number of the most ''savoury'' limericks known - it is also very, very funny due in great part to the author''s dead-pan commentaries and ''geographical index''. Douglas'' erudition effortlessly traverses topics as diverse as the mudflats of Leigh-on-Sea, the dahlias of Central America and the habitat of the Silesian tapeworm.