Present book help to deal with fine or ultrastructure of different cell stages of spermatogenesis and various stages of development of spermatozoa were revealed by transmission electron microscopic observatons (TEM) in the testes and seminal vesicle of amphistone. Also first time describe the ultrastructure of the spermatogenesis and mature spermatoza in an amphistome, species Cotylophoron cotylophorum. The formation of mature spermatozoa from precursor cells called spermatogonia, primary and secondary spermatocytes and spermatid in tested is called spermatogenesis. The transmission electron microscopic observations demonstrated that the testes of spermatogonia were observed. The spermatogonia constitute three cell generations, primary spermatogonia, secondary spermatogonia and tertiary spermatids after successive mitotic divisions. Each spermatogonia cell give rise to a rosette of 32 spermatids. For the first time the present study deals with comparision of ultrastructure of spermatogenesis un different seasonal amphistomes. On the basis of ultrastructural observations, it may be concluded that the ultrastructure of spermatogenesis and the mature spermatozoa in amphistome basically follows the common digenean pattern. The book is very sugnificant as: * Present book is of great importance from mrdico-veterinary point of view. * The book will help in understanding certain histological, cytological and physiological aspects of spermatogenesis of amphistome. * Ultrastructure of spermatogenesis would provide knowledge for chemotherapeutic measures.