282 



Rl^SUMl^ OF UROGENITAL SYSTEM, 



structure are not represented in the diagram. The kidneys 

 thus form at this period an unbroken gland composed of a 

 series of isolated coiled tubes, one extremity of each of which 

 opens into the body-cavity, and the other into the segmental 

 duct, which forms the only duct of the kidney, and communi- 

 cates at one end with the body-cavity, and at the other with 

 the cloaca. 



The next important change concerns the segmental duct, 

 which becomes longitudinally split into two complete ducts in 

 the female, and one complete duct and parts of a second in 

 the male. The manner in v/hich this takes place is diagram- 

 matically represented in woodcut 6 by the clear line x, and 

 in transverse section in woodcut 7. The resulting ducts are 



Fig. 7. 



Diagrammatic representation of a transverse section of a Scyllium 

 Embryo illustrating the formation of the Wolffian and Mullerian 

 dugtb by the longitudinal splitting of the segmental duot. 



I 



-'fnp 



ch 







mc. medullary canal ; mp, muscle-plate ;- ch. notochord ; ao. aorta ; 

 ca V. cardinal vciu ; st. segmental tube. On the one side the section 

 passes through tlio opening of a segmental tube into the body-cavity. On the 

 other this opening is represented by dotted lines, and the opening of the 

 BCgmental tube into the Wolffian duet has been cut through; tc.d. Wolffian 

 duct ; m.d. Miillerian duct. The section is taken through the point where 

 the segmental duct and Wolffian duct have just become separate ; (jr. The 

 germinal ridgo with the thickened germinal epithelium; I. liver; t. in- 

 testine with spiral valve. 



