70 



DEVELOPMENT OF EXTERNAL GENITALIA IN THE HUMAN EMBRYO. 



TABLE 1. Condensed tabulation of specimens exam- 

 ined, arranged in length groups of 10 mm. (length 

 decades). 



structed in order to correlate the development of the internal urogenital organs 

 with that of the external genitalia. 



Only a condensed tabulation of the embryos examined, with the sex classified, is 

 included in the present report, the complete list, including the serial number of each 

 embryo with remarks upon its condition, having been placed on file among the 

 records of the Carnegie Laboratory of Embryology. The sex grouping adopted in 

 this table is based upon the diagnostic features brought out by the investigation. 



Table 1 shows that there is considera- 

 ble variation in the relative frequency of 

 the sexes in each of the length decades 

 and also that there is a greater number of 

 females than males (145 to 84) in the period 

 between 14 and 50 mm. length. This vari- 

 ation in the different groups would indicate 

 that as yet a sufficient number of embryos 

 has not been examined to permit definite 

 deductions concerning the sex-ratio at this 

 period of embryonic life. Conclusions, 

 therefore, will have to be deferred until 

 much more extensive data have been 

 accumulated. 



Critical examination has been made of practically all of the embryos in the 

 collection between the lengths of 14 and 50 mm. About 80 of these, however, 

 have been discarded from present consideration because, owing to mutilation or 

 poor state of preservation, a clear picture of the external genitalia could not be 

 obtained; therefore, no interpretation of sex was possible. Of the older stages 

 (51 to 100 mm. CR) only selected specimens have been studied. The accom- 

 panying list, therefore, includes all the well-preserved embryos between the length 

 of 14 and 50 mm., both sectioned and unsectioned, and a small proportion of the 

 older specimens. 



No attempt was made to identify the sex of embryos smaller than 14 mm., 

 although it is believed that a careful study of a sufficient number of such younger 

 stages will show that the sex differences here pointed out can be traced back to the 

 very beginnings of the genital tubercle. 



HISTORICAL. 



When the early scientists began the study of human embryology with the few 

 specimens that came into their possession, the questions of sex recognition and the 

 relations between the sexes attracted their attention to the study of the external 

 genitalia. When we of the present day consider the paucity of their material, as 

 well as the comparative crudity of their instruments and methods, we can not but 

 be surprised at the accuracy of their observations and conclusions. That there 

 were misinterpretations was due largely to insufficient material and defective 

 apparatus, rather than to faulty observation. 



