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VARIATION in weight of tissues which respond to hormone stimulation may arise from: (1) variation prior to hormone stimulation, (2) variation in amount of hormone to which the tissue is exposed, and (3) variation in sensitivity of tissues of different individuals. Both initial variation and that due to hormone stimulation are affected by genetical and environmental differences between individuals. This report is concerned with early identification of genetic effects on the weight responses of the testes and the comb. These may, or may not, characterize the responses expected from each chicken throughout its life span. The small amounts of androgen or gonadotrophin which may be present in the blood stream prior to 11 days after hatching would appear to be below the threshold for stimulation of comb and testis size in large bodied breeds. Although Breneman (1941) obtained evidence of gonadotropic and androgenic effects on the testes and combs of …

THE function of the bursa of Fabricius, a lymphoendothelial gland of birds, is rather obscure. Glick (1956) emphasizedthe rapid growth of the bursa of Fabricius during the first few weeks after hatching of the chicken. During the past few years, a number of research reports have demonstrated that it is involved in the production of some antibodies in the chicken (Chang, Rheins and Winter, 1957, Rheins and Winter, 1959; Glick, Chang and Jaap, 1956; Glick, 1956, 1960; and Mueller, Wolfe and Meyer, 1960). The involvement of this gland in the stress complex is indicated by the reports of Perek and Eilat (1959, 1960); and Newcomer and Conally (1960). Since the bursa begins to atrophy as early as six weeks after hatching in the Leghorn chicken, its physiologica l function can be of importance only during the first few weeks of its life. The role of this gland in the physiology of the young…