Racial differences in stature and other external features are well recognized in man and in domestic animals, but comparatively few data have been found in the literature on organ size in large and in small animals of closely related races.
Differences in embryonic growth in large and in small races have been studied by Castle and Gregory ('29) and Kaufman ( '30). It has been shown by Castle ('29 and '41) and Riddle et al. ('32) that postembryonic growth is continued for a longer time in larger species. Stockard ( '41) includes data on the size of some of the endocrine glands in his studies of various breeds of dogs. Freudenberger ('32) compared organ weights in large and in small races of rats. Several studies on the skeletal and vascular systems of these two races of rabbits of large and small body size have been made by Sawin and his collaborators and these are summarized by Peck and Sawin ('50) and Sawin ('55). Castle ('41) states that "size genes act chiefly by influencing developmental rate of the embryo . . . To a lesser extent gene action affects groups of organs o r parts independently of general body size. "
Very little is known about comparative organ weights in large and in small races of adult rabbits and this report is an attempt to add to this information.