Abstract1The males of Rana virescens brachycephala rarely attain a body weight above 50 grms. The females (without ovaries) may weigh 75 grams or more.When the average of the largest males is compared with females yielding the same average weight, the males are found to have thelighterbrain and spinal cord.2Spring frogs tend to lose weight rapidly when kept in the laboratory. This tendency diminishes as the season advances toward autumn.3In Rana virescens brachycephala the relative weight of the brain compared to that of the spinal cord decreases as the frog increases in size.4The weight of the leg muscles compared with the weight of the entire frog increases in small frogs up to about 5 grms. of body weight and then slightly decreases as the frog increases in size. In individuals of all sizes, the muscles of the thigh weigh from 1.78 to 1.80 times as much as those of the rest of the leg.5In frogs of all sizes, the sum of the lengths of the leg bones is a nearly constant fraction of the length of the entire frog. The proportional lengths of the several bones are also nearly constant.