374 



COLLEGE ZOOLOGY 



Oviduct ■ 



Kidney- 



Rudimentary ostium and oviduct 



Ostium i 



Esophagus 



Vasa efferentia 



Testis 



Ovary 



Shell gland- 



Urinary duct and 

 vas deferens 



"Uterus" 



Accessory 

 mesonephric duct 



minal vesicle 



nary duct 



Sperm sac 



Cloaca- 



Urogenital papilla 

 Oviduct opening 

 Urinary papilla 



v_iasper 



Male 



Female 

 Figure 250. The urogenital systems of the dogfish shark. 



for capture; it is also used as a weapon of 

 defense. 



The sting ray, Dasyatis (Fig. 251), lives 

 half buried in the sand along the seacoast. 

 Its whiplike tail bears a barbed spine, which 

 is provided with a poison gland; it makes a 

 painful wound when driven into the hand 

 or even through the side of a shoe into the 

 foot. 



The electric eel, Electrophorus electricus, 

 is an eel-shaped fish of the Amazon and 

 Orinoca basins. It is an extreme example of 

 specialization for the greater part of the 



dorsal half of the body behind the head is 

 occupied by the electric organ. This huge 

 mass of electric tissue is made up of about 

 70 columns of electroplates, each containing 

 no fewer than 6000 cells in a series. In water 

 an electric eel four feet long can produce 

 up to 600 volts in potential. The maximum 

 power output is about 1000 watts. The dis- 

 charge of the electric organ may occur a 

 second or more apart and continue for more 

 than an hour without fatigue to the animal. 

 It is suJSicient to disable a fairly large animal; 

 thus it may serve as an effective weapon for 



