GENITO-URINARY SYSTKM OF Till': l-lMl'.HYu. 247 



of the ovary, and has the form of many coiled blind tubules 

 lined with ciliated epithelium. The paroophoron lies more 

 medially, and consists of similar convoluted canals. The first 

 is homologous with the epididyrnis, and the second with the 

 paradidymis in the male. 



Genito-urinary System of the Embryo. 



The first part of the genito-urinary system to appear in the 

 embryo is the Wolffian duct. The origin of this duct is doubt- 

 ful. According to some authors (Hensen, v. Spee), it is derived 

 from the ectoblast. Others believe it arises from the meso- 

 blast; His and Kowalewsky, from the middle plate; and 

 Remak, Kolliker, and Waldeyer, from the lateral plate of the 

 mesoblast. Rensen, Dansky, and others derive it from the 

 coelomic epithelium. It is at first a solid rod of cells, which 

 subsequently develops a lumen lined with epithelium-like cells. 

 Tubules develop from this duct and form the Wolffian body. 

 This embryonic organ was observed first, in 1759, by Wolff, 

 who considered it the embryonic stage of the permanent kid- 

 ney. Rathke (1825) first used the term Wolffian body in 

 connection with this organ in birds, and called the correspond- 

 ing organ in mammals, Oken's body. Jacobson, in 1824, 

 termed it the primordial kidney, and recognized that it 

 excreted uric acid, which was carried into the allantois. 



The Wolffian body of mammalian embryos is a somewhat 

 pyriform body symmetrically placed in the abdominal cavity. 

 In early embryos it is, next to the liver, the largest abdominal 

 organ. It consists of a tubular and a glomerular part. The 

 glomeruli are situated medially, while the coiled tubules form 

 the largest part of the organ. These come off from the Wolff- 

 ian duct at right angles to it, and after a considerable coiling 

 are connected with the glomeruli by means of end dilatations 

 similar to the Bowman's capsules of the permanent kidney. 

 In the human embryo the tubules have a somewhat S-shaped 

 course. In the pig's embryo, on the contrary, the tubules are 

 much convoluted. Their exact course has been determined 

 (MacCallum) by means of injections into the Wolffian duct, and 



