RESUMEN
Yellowish myotis, Myotis levis, is a seasonal, epididymal sperm-storing Neotropical vespertilionid. In the dry season, males show simultaneous testis regression and sperm storage in cauda epididymis, enabling them to mate during this season. In this study, we investigated seasonal variations in body mass, diameter and height of seminiferous tubules and nuclei of Leydig cells in a population of southeastern Brazil. We also determined the frequencies of the stages of the seminiferous epithelium cycle (SEC) of mature individuals of this population. Body mass and diameter of Leydig cell nuclei showed no significant differences between dry and rainy seasons and stages of annual reproductive cycle; however, all other morphometric parameters varied significantly. The relative cumulative frequency of pre-meiotic stages of the SEC (1-3) was 51%, of meiotic stage (4) was 2% and of post-meiotic stages (5-8) was 47%. We confirmed that the yellowish myotis presents seasonal sperm production as revealed by testis regression and epididymal sperm storage during the dry season.