Platyhelminthes are also known as flatworms because they are worms with a flat body. This is the main external morphological feature that differentiates them from nematodes (roundworms).
Even though 85 percent of kidney stones are small enough to pass during urination, fewer than 50 percent of patients chose this option. A person with a normal-size ureter can usually pass a kidney stone with a diameter less than 5 mm (about 3/16 of an inch) without significant pain or risk of kidney damage.
As of August 2006, the most kidney stones ever passed naturally was 5,704 by Canadian Donald Winfield. The largest number removed through surgery was 728, during a three-hour operation upon Mangilal Jain of India, on January 27, 2004.