FIGURE 1.

Testicular descent and scrotum/mammary region development in the fat-tailed dunnart. From D2–8 PP, the gonads are intra-abdominal, while the developing scrotal bulge is visible in males by D8 (A, C, D, E–G). At D2, there is very little differentiation of the epidermis that will later form the scrotum in males or the mammary glands and pouch in females (B). In D8 females, the mammary primordia are well differentiated, and mammary buds have started to form (H). By D30, the testes are descending transabdominally, and the scrotum is fully formed (I). Females have visible teats and a pouch lip by D30 PP (J). By D50 PP the testes are inguinal, and the scrotum/pouch is are clearly visible (K, L). Testes fully descend into the scrotum by D60 PP. A: anterior, P: posterior, Go: gonad, Gu: gubernaculum, Me: mesonephros, Mb: mammary buds, Ph: phallus, Po: pouch, T: testis, and Te: teat.