Words can hardly express my profound sense of gratitude to my beloved guide Dr. M.M. Shahul Hameed, M.Sc., Ph.D., Professor and Head, P.G. Department of Zoology, Jamal Mohamed College, Tiruchirappalli, without whose guidance, inspiring and valuable suggestions, close supervision, efficient instruction and constant encouragement, I would not have submitted this thesis in time. I extend my gratitude to Dr. P. Shahul Hameed, M.Sc., Ph.D., former Professor and Head, P.G. Department of Zoology, Jamal Mohamed College, Tiruchirappalli for his constant encouragement during the tenure of my research. I am immensely grateful to Dr. A. Sadiq Bugari, M.Sc., Ph.D., Lecturer in Zoology, P.G. Department of Zoology, Jamal Mohamed College, Tiruchirappalli for his constant encouragement. I am very grateful to Dr. S. Selvasekara Pandian, Head, Mr. G.M. Brahmanandhan and Mr. D. Khanna, Ph.D. Scholars of Solid State and Radiation Physics Laboratory, Department of Physics, Bharathiyar University, Coimbatore for their valuable help in learning the analytical techniques of radionuclides and permitting me to make use of the library to collect references.