XXI. Despite being well into the twentieth century, the laboratory mouse has been found by an unknown organ. So far it has been believed that mice had a single roof - the thymus is an organ of the immune system located on the chest, but there are mice having a second in the neck. The discovery was made by researcher Rodewald of the University of Ulm (Germany), Hans-Reimer Rodewald, who has acknowledged that he has been unbelieving for two months. The controversy is on the table, since the discovery will put up several beliefs about immunology.