512 



DEVELOPMENT OF ELASMOBRANCH FISHES. 



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 communicates 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 which this takes place is diagrammatically 

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

 section in woodcut 7. The resulting ducts are the (i) Wolffian 

 duct dorsally, which remains continuous with the excretory 



FIG. 7. 



DIAGRAMMATIC REPRESENTATION OF A TRANSVERSE SECTION OF A SCYLLIUM 

 EMBRYO ILLUSTRATING THE FORMATION OF THE WOLFFIAN AND MULLERIAN 

 DUCTS BY THE LONGITUDINAL SPLITTING OF THE SEGMENTAL DUCT. 



mp 



me. medullary canal ; mp. muscle-plate ; ch. notochord ; ao. aorta ; ca v. 

 cardinal vein ; st. segmental tube. On the one side the section passes through the 

 opening of a segmental tube into the body-cavity. On the other this opening is 

 represented by dotted lines, and the opening of the segmental tube into the Wolffian 

 duct has been cut through; w, d. Wolffian duct; m. d. Mullerian duct. The 

 section is taken through the point where the segmental duct and Wolffian duct have 

 just become separate; gr. The germinal ridge with the thickened germinal 

 epithelium ; /. liver ; i. intestine with spiral valve. 



