Mo. Const. art. III, § 18

Each house shall appoint its own officers; shall be sole judge of the qualifications, election and returns of its own members; may determine the rules of its own proceedings, except as herein provided; may arrest and punish by fine not exceeding three hundred dollars, or imprisonment in a county jail not exceeding ten days, or both, any person not a member, who shall be guilty of disrespect to the house by any disorderly or contemptuous behavior in its presence during its sessions; may punish its members for disorderly conduct; and, with the concurrence of two-thirds of all members elect, may expel a member; but no member shall be expelled a second time for the same cause. [Effective - 27 Feb 1945 , see footnote]