In spite of numerous reports on the embryologic study of the complicated genitourinary system published since the time of Aschoff (1894) and of Keiben (1896). There are a number of problematic points here and there regarding the so-called posterior urethra. The fact that the male urethra is a complex organ accompanied by vas deferens and other glandular ducts markes if necessary to investigate the female urethra in order to gain knowledge concerning the native morphology of this organ.
The author has made extensive observation on the female urethra from the early stage of its embryonic development, but if was soon found that comparisor with the adult organ was requisite since this organ in the embryo or fetus is still quite immature. The organs obtained from fetuses from the third to the tenth month of gestation were cut transversally and the whole length of the structure was investigated by making sagittal sections. Likewise the adult organ was prepared in the same manner, the sections having been prepared in either sagittal or horizontal planes.
A. Development of the urethra
The cranial portion of the ventral rudiment of cloaca develops into the bladder and primary urethra, while its caudal portion forms the urogenital sinus. The primary urethra is the portion from the mesonephric duct to the orifice of the paranephric duct, corresponding to the urethroprostatic part to the opening of the ejaculatpry duct in the male, but in the female it forms the entire length of the urethra.
The author made observations on the preparations taken chiefly from 3-month fetuses. At first the formation of a small duct lumen is noted at the pelvic portion of the so-called urogenital sinus, and then a stream of mucous membrane is seen representing the urethra-bladder in the sagittal cut sections. In 4-month fetuses the urethral cavity is formed in various, morphologic characteristics acording to the locations studies. Furthermore, the structure and course of mucous epithelium could also be observed. At this stage, the bladder is a relatively large structure but the urethra is narrow, small and short. However, the paraurethra duct can be seen already as a budding structure or a small cord-like existence of the mucous membrans. In the sagittal sections, the nature of the structure from the bladder to the external opening of the urethra could be well observed. In the preparations of 5-month fetuses these relations show a greater degree of development and the nature and structure of the epithelium and the distinct presence of paraurethral ductt were observed. It was possible to observe almost completely in fetuses from 6 to 7 months of gestation the condition of the epithelium, the size and distribution of the paraurethral duct and its ramifications. During the 8-9-10 months of fetal age all the findings approach those of adults, except a few specific respects suggesting the immaturity in some details.
The author thus has been able to elucidate the morphology of the urethra and epithelial structure, but distribution and morpholic structure are so extremely complicated that its difficult to describe in words. Hence the findings have been expressed by means of models. Each of these models localizes the position and length of the structures by following the cross sections of each fetuses (See the text and table I.).
B. The paraurethral ducts
In 3-month fetuses it is already possible to observe the formation of duct spaces and in those of 4-months the invagination of mucous epithelium, its plication mucous budding and small duct space. During 5-6 month of gestation the course, morphology and ramifications of the paraurethral duct can be demonstrated, and during 7-8-10 months the paraurethral duct continues to become more and more complex by infolding of the mucous membrane.
C. The mucous epithelium
Although the urethral epithelium in the female is remarkably characteristic, the main portion consists of several layers of short

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