Knowledge of the structural complexities of the testis has advanced at a slower pace than that for other organ systems of the body. In part the difficulty in understanding the morphology of the normal testis stems from the fact that spermatogenesis is an extremely complex process, not lending itself to simple classification schemes. Although the spermatozoon is a relatively simple cell, the process by which it is formed usually takes months to complete. Once a germ-cell reaches a certain phase of development it undergoes a continual and irreversible process of differentiation. During its modification to become a spermatozoon, a cell may be referred to as a spermatocyte or a spermatid, but it should be realized that this cell is undergoing continuous modification and that there are a multiplicity of morphological and functional changes that take place in this process. By segregating developmental changes that occur in relatively short periods of time, cleverly devised “roadmaps” for understanding, classifying, and studying spermatogenesis have been developed [cf Leblond and Clermont, 19521. Now, short periods in the life span of a cell can be segregated by morphological criteria in a very precise manner. Only recently have classification schemes been employed at the ultrastructural level, thus allowing fine structural relationships of cells within the seminiferous tubule to be studied. process has been the difficulty involved in adequately preserving the testis for highresolution light (plastic section) and electron microscopy. Christensen [19651, who was particularly interested in Leydig cells, developed a method by which the testis could be adequately preserved. This method involved perfusion of substances directly into the testicular artery. Subsequent improvements in this perfusion method and the fixatives to be utilized have been made in several laboratories [Vitale-Calpe et al, 1973; Forssman et al, 1976; Russell and Burguet, 19771. At the present time, the morphological results obtained for the testis are comparable to those of other tissues of the body. The lower resolution paraffin-embedding material used for light microscopy has in many instances