THE UEO-GENITAL SYSTEM. 103 



Wolffian Body in the evolution of the vertebrates. Its presence 

 in the human embryo and in the embryonic stages of the three 

 great classes of higher vertebrates, with the presence of many 

 curious stages in the development of their genito-urinary system, 

 can be explained only by the fact that these higher forms are 

 descended from ancestors of the lower. 



In Fig. 79 the Wolffian body, such as occurs in the frog, is 

 represented diagrammatically and it corresponds in structure to the 

 Wolffian body which appears in the human embryo. Each body is 

 made up of a main duct and a series of tubules. In the frog, as 

 in the human embryo, the hind gut ends in a dilatation, the 

 cloaca. In the cloaca open the rectum, allantois, and the two 

 Wolffian ducts — right and left. In the frog, the Wolffian bodies 

 lie on each side of the spine, their anterior ends reaching forwards 

 to the region of the heart. Each duct is joined by numerous 

 convoluted tubules — the Wolffian tubules. Each tubule is fur- 

 nished with a glomerulus at its blind extremity and in most 

 features agrees with a secretory tubule — such as are seen in the 

 permanent kidney. These tubules secrete the urine ; the Wolffian 

 duct conveys the urine from the tubules to the cloaca. The anterior 

 tubules, however, loose their secretory function and become associ- 

 ated with the genital gland. In the male frog they convey the 

 spermatozoa to the Wolffian duct, which thus carries both urine, 

 and spermatozoa. In the female, the genital Wolffian tubules are 

 connected with the ovary but are quite functionless (Fig. 79). 



The Wolffian Body in the Human Embryo. — At the 

 beginning of the second month of foetal life, the Wolffian body is 

 well developed : by the end of that month it has become vesti- 

 gial, the only parts remaining being those connected with the 

 genital organs. It projects as a ridge from the lumbar and 

 dorsal regions on each side of the mesentery, extending, on 

 each side of the spine, from the posterior cervical region, where 

 the diaphragm is developed, to the pelvis behind, where the 

 ridges become approximated (Fig. 80). To its inner side, in 

 the lower dorsal region, lies the genital ridge. The genital and 

 the Wolffian bodies have each its own mesentery but these 

 two mesenteries have a common attachment — the common 

 uro-genital mesentery (Fig. 80). On section the Wolffian ridge 

 is seen to be made up of convoluted tubules terminating at 



