The annual cytological changes during spermatogenesis and the ultrastructure of the male germinal epithelium were investigated in European wall lizards, slider turtles, and American alligators. Wall lizards, alligators, and slider turtles all have the same type of temporal germ cell development. The majority of germ cells within a cross-sectional area of seminiferous tubule progress as a single population through the three phases of spermatogenesis. This temporal development leads to a single spermiation event at the end of germ cell development. Consistent spatial relationships (stages) between germ cells, which are found in mammals and birds, do not exist in these three reptiles.; Wall lizards have a prenuptial pattern of spermatogenesis, where sperm development begins immediately prior to and continues through the months of breeding (April--following June). Alligators also have a prenuptial pattern of sperm development; however, the speed of their germ cell development occurs at an accelerated rate compared to the wall lizard and slider turtle. Spermatogenesis in the alligator begins in February and is completed by June, a five-month period. The slider turtle exhibits a postnuptial germ cell development that starts shortly after mating (May) and is completed by late fall (November). Their common temporal progression of germ cells through spermatogenesis within a tubular testis represents a transitional model that may be evolutionarily significant.; Junctional complexes are observed in the slider turtle and wall lizard and include desmosome-like, gap-like, and tight junctions. All junctions in both species show ectoplasmic specializations, including subsurfaces densities, smooth endoplasmic reticulum (SER), and 7--9nm filaments. However, the SER is less organized and further away from the junctional complexes and the 7--9nm filaments are not as prominent as those seen in mammals. Tight junctions in both are also effective barriers to lanthanum penetration. Lanthanum surrounded spermatogonia and preleptotene cells, but it never penetrated to deeper meiotic or spermiogenic cells at any time during the year. In all samples observed in this study the barrier was never compromised, similar to mammals. The inconsistency and unorganized association of the SER and the 7--9nm filaments suggest that reptilian junctional complexes are more complicated than amphibians but simpler than mammals.
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