Fig. 8. Correlation between a gestational age and a topographical relation between the ureter and the Wolffian duct or vas deferens. One dot (a simple dot or a dot with circle) corresponds to one specimen. Thirty-two of the 35 specimens observed were evaluated because, in 3 specimens, a complete set of serial sections were not available. The dot with circle indicates a fact that, in the specimen, bladder smooth muscles as well as urethral rhabdosphincter muscles were evident. Depending on drastic development and growth of these muscles, the descent of the vas deferens rapidly occurs at 10–11 weeks. This change are not correlate with individual variations (Figs. 3,4,5,6,7) in the transverse shape and size of the urogenital sinus, bladder and urethra.