neural spine 



ligament 



neural arch 



spinal cord 



sheath of notochord 



subchordol rod 



dorsal aorta 

 kidney 



postcardinol (subcardinal) 



rib 



nephric duct 



coelomic duct 



rete testis in mediastinum 



testis 



spiral valve 



Figure 10-47. Cross section of male of Acipenser fu/vescens showing connection (on reader's 

 right) between the nephric duct and the coelomic duct. 



Squalus there is a short, bladder-Uke expansion of the nephric 

 duct here. The nephric ducts join as a urinary sinus, which 

 also serves the ureters when present, and this opens through 

 a papilla into the cloaca. From the cloaca the spermato- 

 phores (bundles of sperm) are forced by the action of 

 siphons, muscular sacs underlying the skin and extending 

 forward from the cloaca, through the grooves of the claspers 

 into the cloaca of the female. 



In some sharks a rudiment of the Miillerian duct enters 

 the cloaca near the nephric duct; this is the vagina mascu- 

 lina. 



THE FEMALE The ovary is generally shorter than the testis. 

 Usually there are right and left ovaries, but in some sharks 

 the left may be rudimentary (Scyllium, Pristiophorus, Carcha- 

 rias, Galeus, Mustelus, ^gaena). An epigonal organ may be as- 

 sociated with the ovary {Scyllium, Heplanchus). The eggs are 

 shed into the body cavity and carried to the exterior through 

 the Miillerian ducts. The common funnel of these ducts lies 

 at the anterior end of the body cavity, below the esophagus 

 and just behind the heart. In some sharks there are paired 

 ostia in the region of the pronephros. The Miillerian duct 

 consists of the usual segments: funnel, tube, isthmus, uterus, 



and vagina. In oviparous forms there are two specialized 

 zones in the tube which secrete albumin, and a horny shell 

 to enclose the egg; these zones form the nidamental gland. 

 Fertilization apparently occurs in this area. Squalus is vivip- 

 arous as are many sharks. In these the fertilized egg under- 

 goes development in the uterus, most of the posterior half of 

 the oviduct. The developing young may recieve nourishment 

 from the maternal tissues in some species (metaviviparous). 

 The vagina is the terminal section connecting with the 

 cloaca; it opens dorsolateral or dorsal to the urogenital sinus. 



Holocephalan The testes of the male chimaerid lie far for- 

 ward in the body cavity (Figure 10-48 E). The efferent ducts 

 differ in that they are more numerous and form an anasto- 

 mosing network in the mesorchium. The epididymis is well 

 developed as is the Leydig's gland. The nephric duct is partly 

 separated from the ureters and its terminal half is expanded 

 as a glandular ampulla. Several ureters open into the am- 

 pulla, along its length, and into the urinary sinus formed by 

 the fused posterior ends of the nephric ducts. The urinary 

 sinus opens by a small pore behind the anus. Distinct Miil- 

 lerian ducts occur in the male. These can be followed from 

 the region of the heart, along the ventrolateral walls of the 



334 



THE UROGENITAL SYSTEM 



