Offspring of 6 wild, male (brown-coated) dump rats ( Rattus norvegicus) and laboratory albino females were compared with the offspring of albino rats on several tissue and muricide measures. At weaning, the 48 hybrid pups (all brown-coated), both vocalized and bit the experimenters' gloves; these behaviors were not apparent in the 40 albino pups. Adult hybrid rats did not kill significantly more mice than albino controls. Although hybrid rats had significantly lighter (ω2 = 55%) wet thyroid weights than albinos, they did not differ in spleen, thymus, adrenal, or body weights.
