Spermatogenesis is a basic biological process of great significance, but its exploration has been generally unsystematic and often inconsistent throughout the 127 years since K#{246} lliker (48) discovered that spermatozoa develop from cells of the testis. At present, the field is anything but fashionable among scientists. The Biological Abstracts of 1967 contain

125,027 titles. The word spermatogenesis(or-genic) is found in 99 of these; spermatid (s), spermiogenesis, or spermateleosis in 21; spermatocyte (s) in 12; spermatogonia (l) in 10.(For comparison, 276 titles contain the word lymphocyte I-cytic 1 and 1127 the word DNA.) Of the 142 titles pertaining to some aspect of the development of the male gamete, only approximately 107 contribute in any conceivable way to the considerations of the present review. The 106 titles in which the word spermatozoon or spermatozoa appears are not pertinent to our discussion but indicate a flurry of electron microscopic studies of this highly differentiated cell. Another indication of the relative neglect of our subject is the fact that a general review of animal spermatogenesis need not draw on more than approximately 500 significant references since 1841, as I know from personal experience. Finally, such a review leads to the discovery that spermatogenesis has been studied in very few species. There are no more than 50 of 700,000(84) insects, 40 of 100,000 molluscs and 40 of 43,000 vertebrates for which a coherent and detailed ac-