. Contributions to embryology. Embryology. 72 DEA'ELOPMENT OF EXTERNAL GENITALIA IN THE HUMAN EMBRYO. which show the shorter urethral groove that I have found to be characteristic of female embryos, no special description is given ot these structures. In fact, he realized that for the investigation of the development of the external genitalia a large series of embryos was necessary, and this portion of his paper is for the most part devoted to a plea to his colleagues for more specimens. While I realize that I have been more fortunate than any of my predecessors in having at my disposal a larg
. Contributions to embryology. Embryology. 72 DEA'ELOPMENT OF EXTERNAL GENITALIA IN THE HUMAN EMBRYO. which show the shorter urethral groove that I have found to be characteristic of female embryos, no special description is given ot these structures. In fact, he realized that for the investigation of the development of the external genitalia a large series of embryos was necessary, and this portion of his paper is for the most part devoted to a plea to his colleagues for more specimens. While I realize that I have been more fortunate than any of my predecessors in having at my disposal a larger and more complete series of embryos, I still would reiterate Keibel's plea for more material; because it seems that the more specimens one has at his disposal, the more one realizes the need of additional material in order to study some of the points concerning which there is still a conflict of opinion. In 1904 Herzog pointed out that the direction of the phallus made it possible to recognize the sex of an embryro at about the beginning of the third month, in- stead of towards its close. This difference in direction he showed to consist in a greater caudal decurvation of the female phallus, while that of the male remained more nearly at right angles to the axis of the body. His series consisted of 16 embryos, varying in length from 20 to 190 mm. Of these, he figures the external genitalia of only 9, none of which bring out very clearly his point of directional dif- ference of the phallus. Some excellent figures of the external genitalia are given by Otis (1906), although the discussion of the genitalia does not form a logical part of his paper. CLANS AREA EPITHEUAL TAG LATERAL BUTTRESS URETHRAL GROOVE URETHRAL FOLDS *V-ANAL TUBERCLES. — 4 t,[ UTEAL FOLD Text-Figure 1.—Drawing of external genitalia of an embryo mm. long (Specimen No. 492), illustrating the genital-tubercle period. X 25. From 1890 to 1907 a number of valuable contributions upon the development of the
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