452 CHARLES H. SWIFT 



On examining with a microscope a section through the anterior 

 third of the sexual region of the Wolffian body the following 

 facts concerning the genital anlagen may be observed. 



Each gonad appears as a rounded hillock on the medial surface 

 of the mesonephros, and is separated from its fellow by the 

 mesentery. Even at the first glance it will be noticed that the 

 gonad is composed of three tissues (fig. 1) . The epithelium cover- 

 ing the gonad is a single layer of elongated prismatic cells. This 

 epithelium is the germinal epithelium of Bornhaupt and Waldeyer 

 (70) and of succeeding authors. This epithelium is not confined 

 sharply to the gonad, but, beyond its medial and lateral bound- 

 aries, merges with the flat coelomic epithelium (fig, 1). At this 

 time and in the two later stages the germinal epithelium covers 

 the mesentery for some distance before it disappears. The 

 germinal epithelium commences to differentiate from the coe- 

 lomic epithelium when the embryo is 3^ days old so at this time 

 it is well developed. 



Under this germinal epithelium is a compact mass of tissue, 

 the cells of which, although more closely packed, resemble those 

 of the general embryonic mesenchyme. This compact tissue 

 makes up the mass of the gonad, occupies the concavity of the 

 germinal epithelium, and hence gives rise to the rounded form 

 of the germinal hillock. 



If the section happens to be rightly situated, the mesenchyme 

 material under the germinal epithelium will be observed to 

 extend into a cord or strand, which runs obliquely towards a 

 Malpighian corpuscle. According to Firket ('14) there are six- 

 teen of these cords and they together with the tissue under the 

 germinal epithelium make up the urogenital connections or 

 "organ of Mihalkowics" of Sainmont ('05). There has been 

 much discussion as to the origin of these cords of urogenital 

 union, as to whether they are derived from peritoneal epithelium, 

 the capsules of the Malpighian corpuscles or the mesenchyme. 

 My preparations from embryos of this age, that is 90 hours, and 

 from one of 84 hours, would seem to show that the cords of 

 urogenital union are derived from the mesenchyme. This is at 

 variance with the opinion of Sainmont ('05) who described them 



