This book gives a detailed age-related baseline data on the gross, histological and histochemical development of thymus, spleen and bursa of Fabricius in Hansli chicken and Vencobb broiler chickens. This could be correlated with various molecular techniques in characterization of the age related immunogenic potency of these two breeds of poultry. Further, this type of research study can be mingled with advanced molecular techniques and could also be carried out in other indigenous breeds of poultry of India to establish a baseline immunogenic data and basing on the outcome, they could be recommended to the farmers for rearing purpose.