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efferent vessels or epibranchials (one from each loop) pass 

 inwards and obliquely backwards to unite in a median 

 Irunk, the dorsal aorta, which passes backwards to supply 

 the body. The principal branches of the dorsal aorta 

 are a pair of subclavians, a coeliac to the stomach and liver 

 and pancreas, mesenteries to the intestine ; and its posterior 

 continuation is the caudal artery. 



Describe the Urino- genital System of (1) the Male, and (2) 

 the Female Dogfish (Scyllium). 



(1) The kidneys are situated in the abdominal cavity, 

 one along each side of the vertebral column, and above the 

 peritoneal lining. The front portion of each is the meso- 

 nephros (well developed) ; the hind portion is the rneta- 

 nephros. The Wolffian ducts (vasa deferentia), on the 

 ventral surface of the kidneys, are sinuous ; and each 

 dilates posteriorly into a vesicula seminalis, opening into 

 the urinogenital sinus (i.e., the united dilated ends of two 

 sperm sacs beneath the seminal vesicles ; these sacs, blind 

 in front, open behind into the cloaca). The ureters, each 

 formed from the union of about five metanephric ducts, 

 open into the urinogenital sinus. 



The two elongated testes are attached to the dorsal wall 

 of the abdominal cavity by folds of peritoneum, and are 

 united posteriorly. Each testis is connected with the 

 anterior end of each mesonephros by several fine ducts, 

 the vasa efferentia. Only vestiges of the Miillerian ducts 

 are present. Associated structures are the copulatory 

 claspers of the pelvic fins. 



In the Skate ( Raia) the renal and reproductive organs 

 are similar ; but the testes are not united posteriorly. 



(2) The mesonephros is rudimentary ; the Wolffian ducts 

 are straight, and their dilated ends, the urinary sinuses, 

 open into the cloaca. The metanephric ducts (ureters) 

 open separately into the urinary sinuses. 



The single ovary, when mature, has a sacculated appear- 

 ance. The two large oviducts (Miillerian ducts), which 

 are not connected to the ovary, are united anteriorly in 

 front of the liver (falciform ligament), and there open, by 

 one common slit-like opening, into the abdominal cavity. 

 An anterior distension of each oviduct is the oviducal gland, 

 which secretes the horny egg-capsules (" Mermaid's purse "). 

 The oviducts, united at their ends, have a large common 

 opening into the cloaca, behind the anus. 



Q 



