EENAL AND REPRODUCTIVE SYSTEMS 245 



it about equals in length. It ends blindly in front, 

 and dilates behind to form the urino-genital sinus. 

 Dissect awoA)^ the sperm sac from the mesonephric duct, 

 and follow it hack to the urino-gerdtal sinus. 



6. The urino-genital sinus of each side is the posterior 



end of the sperm sac, into which open the vesicula 



seminalis and the ureter. About a quarter of an 



inch behind these openings the sinuses of the two 



sides unite, and then open into the cloaca by a small 



aperture at the apex of the urino-genital papilla, 



which is situated immediately behind the opening of 



the rectum. 



Find the opening at the apex of the urino-genital papilla : 



pass a seeker through the opening, and forwards along the 



u/rino-gerdtal sinus and sperm sac of one side : slit up the 



ventral wall of the sinus and sac along their whole length : 



examine, and pass a seeker into the orifices of the vesicula 



semmalis and ureter. 



7. The metanephric ducts are usually five in number on 



each side ; they arise from the outer border of the 

 ventral surface of the metanephros at intervals along 

 its length. The four anterior ducts, after a short 



Pig. 55. — Scyllium canicula. Dissection of a male from the ventral 

 surface, to show the renal and reproductive systems. The left 

 lobe of the liver and the alimentary canal from the oesophagus to 

 the rectum have been removed. The excretory organs of the left 

 side only are shown. An arrow is passed through the left abdominal 

 pore into the abdominal cavity, (a. m. m.) 



Pio. 56.— Further dissection of the renal and reproductive organs. 

 The liver and the greater part of the testis have been removed. 

 The right metanephric duct is shown in its natural position ; the 

 left duct has been displaced outwards. The urino-genital sinuses of 

 both sides have been laid open. (a. m. m.) 



AP, abdominal pore. CP, olasper. CB, groove in clasper. OS, aao con- 

 tinuous with groove in clasper. E, oesophagus. F, pelvic fin. G, gill-slit. 

 H, testis. L, liver. P, abdominal opening ol pronephrio ducts. PD, rudi- 

 mentary pronephrio duet. PQ-, pelvic girdle. B, rectum. EGr, rectal gland. 

 BO, opening of rectum into cloaca. S, mesonephros. SD, mesonephric duct 

 or vas deferens. SO, opening of mesonephric duct into urino-genital sinus. 

 SS, sperm sac. T, metanephros. TD, metanephric duct or ureter. TD' 

 ducts from binder part of metanephros, joining the ureter as it reaches the 

 urino-genital sinus. TO, opening of ureter into urino-genital sinus. TJP, 

 urino-genital papilla. TJS, urino-genital sinus. VE, vasa efferentia. VS, 

 vesicula seminalis, the dilated hinder end of the mesonephric duct. 



