287.130.  Employer's liability joint and several — contribution allowable. — If the injury or death occurs while the employee is in the joint service of two or more employers, their liability shall be joint and several, and the employee may hold any or all of such employers.  As between themselves such employers shall have contribution from each other in the proportion of their several liability for the wages of such employee but nothing in this chapter shall prevent such employers from making a different distribution of their proportionate contributions as between themselves.