ELASMOBRANCHII 



437 



and three semicircular canals. An endolymphatic canal leads from 

 the dorsal exterior into the lower part of the vestibule the sacculus. 

 A posterior pouch of the sacculus is the lagena, which is considered 

 the foreranner of the cochlea of higher vertebrates. The ear serves 

 the sense of equilibration in the fish. 



A canal extends along the side of the body in the lateral line and 

 forward onto the head, lying just beneath the skin. This is the 

 lateral line system. On the head there are some pores with tubes 

 extending beneath the skin to small bulbs called ampullae of Loren- 

 zini. The function of the lateral line system ajid these ampullae 

 is perception of water pressure and vibrations. 



Endolymphatic duct 



Anterior semi- 

 circular canal 



Utriculus 



Posterior semi- 

 circular canal 



Horizontal semi- 

 circalar canal 



Recessus utnculi L ^ \^ ^^^ '-'"?^'^ 



Sacculus 

 Fig. 236. — Diagram of lateral view of left internal ear of Reniceps tiburo. 



Urinog-enital System 



The kidneys are thin, slender organs extending along the dorsal 

 body wall, one on each side of the vertebral column. The posterior, or 

 caudal, portion functions in excretion. There is an accessory meso- 

 nephric duct embedded in each kidney which carries urine to the 

 urinogenital sinus of the male, and the Wolffian duct serves as the 

 urinary duct of the female, emptying into the urinary sinus. A 

 papilla leads from the sinus to the cloaca in both. In the male sper- 

 matozoa are produced in the testes, carried by several vasa efferentia 

 through the mesochorium to the convoluted cranial portion of the 

 Wolffian duct, the epidid^Tnis of each side, which continues poste- 

 riorly as the vas deferens. This tube enlarges to become the semincH 

 vesicle and continues into the inflated sperm sac which is directly con- 

 nected with the urinogenital sinus. The spermatozoa then pass out 

 through the papilla to the cloaca, thence to the outside by way of 



