The role of certain morphological structures in the various modes of of flight occurring in 12 species of bats was studied. Techniques for determining the volumes of the entire body and of individual flight muscles, shapes of wings and surface areas of flight membranes were developed and appropriate measurements taken. It was found that the surface areas of flight membranes, within groups having similarly shaped flight membranes, increase by approximately .66 times as the total volume of the body increases once. Futhermore, the surface area of the flight membrane per volume of the entire body is greater in those species with a lower aspect ratio than in those species with a higher aspect ratio. The total volume of all the ventral thoracic flight muscles increases approximately 1.16 times as the total body volume increases once, irrespective of the shape of the flight membrane. The sum of the volumetric proportions of the pectoralis major and serratus magnus (inferior) remains approximately constant.