John Bruce MacCallum 



347 



In a human embryo, CLXIV/ 3.5 mm. in length, possessing 19 myo- 

 tomes (probable age 2 J weeks), the Wolffian duct is found in an early 

 stage of its development. It is in close connection with the coelomic 

 epithelium in many places; and at its anterior extremity is evidently a 

 direct turning in of the lining of the crelom. Fig. 1 A. The duct con- 

 sists of a rod of cells ending anteriorly in a depression or groove. This 

 is shown on the left side of Fig. 1; while on the right side the duct is 



cut more posteriorly and shows already some 

 indication of the formation of a lumen. 

 Examined closely, the organ is found to con- 

 sist of two parts, an anterior, and a posterior 

 division. The anterior part begins opposite 

 the 6th myotome, and ends opposite the 9th. 

 The posterior part begins opposite the 10th 

 myotome and extends throughout the rest of 

 the body to the level of the last myotome. 

 This is shown diagrammatically in Fig. 2. 

 The anterior part, A., is a simple rod-shaped 

 mass, of cells possessing a small lumen at the 

 anterior end opening into the body cavity, as 

 shown in Fig. 1. The posterior part, W. B., 

 extends backward parallel with the last nine 

 myotomes; and at 13 places on its course it is 

 thickened to form rounded masses, from a few 

 of which there project lateral 

 outgrowths. These are the be- 

 o-innings of the Wolffian tubules, 

 W. T. At this stage there is no 

 indication whatever of glomeruli. 

 The significance of these two 

 parts of the urinary apparatus is 

 not clear. One is tempted to 

 consider the anterior mass of 

 cells as in some way related to the pronephros of lower animals; and 

 the posterior mass, as the developing Wolffian body. The fact that the 

 anterior mass possesses a lumen which opens into the body cavity would 

 seem to support this idea, as this is the case with the pronephric tubules 



Fig. 3. Diagrammatic reconstruction of 

 urinary apparatus in human embryo CLXIV. 

 A ., anterior rep-ion of apparatus : W. B., Wolf- 

 fian body ; W. T., tubules. The myotomes are 

 numbered. 



1 The Roman numerals refer to embryos in the collection of human embryos 

 belonging- to Dr. Mall, in the Anatomical Laboratory of the Johns Hopkins 

 University. 



