694 



ELASMOBRANCHIL 



in the fact of the anterior undivided part of the segmental duct, 

 which forms the front end of the Miillerian duct, being shorter, 



trd/ 



FIG. 389. FOUR SECTIONS 

 THROUGH THE ANTERIOR 

 I'ART OF THE SEGMENTAL 

 DUCT OF A FEMALE EMBRYO 

 OF SCYLLIUM CANICULA. 



The figure shews how the 

 segmental duct becomes split 

 into the Wolffian or meso- 

 nephric duct above, and Miil- 

 lerian duct or oviduct below. 



wd. Wolffian or meso- 

 nephric duct; od. Miillerian 

 duct or oviduct ; sd. segmen- 

 tal duct. 



FIG. 388. DIAGRAMMATIC REPRESEN- 

 TATION OF A TRANSVERSE SECTION OF A 



SCYLLIUM EMBRYO ILLUSTRATING THE 

 FORMATION OF THE WOLFFIAN AND MlJL- 

 LERIAN DUCTS BY THE LONGITUDINAL 

 SPLITTING OF THE SEGMENTAL DUCT. 



me. medullary canal; mp. muscle-plate; 

 ch. notochord; ao. aorta; cav. cardinal 

 vein; st. segmental tube. On the left side 

 the section passes through the opening of 

 a segmental tube into the body cavity. On 

 the right this opening is represented by 

 dotted lines, and the opening of the seg- 

 mental tube into the Wolffian duct has 

 been cut through; iv.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; gr. the germinal ridge with the 

 thickened germinal epithelium ; /. liver ; 

 i. intestine with spiral valve. 



and in the column of cells with which it is continuous being 

 from the first incomplete. 



The segmental tubes of the mesonephros undergo further 

 important changes. The vesicle at the termination of each peri- 

 toneal funnel sends a bud forwards towards the preceding 

 tubulus, which joins the fourth section of it close to the opening 



