500 



COMPARATIVE ANATOMY. 



The Fishes which are provided with these organs belong to 

 the genera Torpedo and Narcine among Rays, Gymnotus among 

 Eels, and Malapternrns among the Siluroids; Mormyrus also has 

 similar organs. There is a pseudo-electric apparatus in Raja. 



Although these 

 tr: v j t . organs differ greatly 



from one another in 

 position, and in their 

 broader anatomical 

 details, in the dif- 

 ferent genera, they all 

 agree in being com- 

 posed of " alveoli " of 

 various forms, which 

 are bounded by con- 

 nective tissue, and 

 filled with a jelly-like 

 substance. The nerves 

 pass to one surface of 

 these alveoli, where 

 they form fine net- 

 works, and give rise, 

 finally, to an ' ' electric 

 plate/' which repre- 

 sents the ends of 

 these nerves. 



The relation of 

 this plate to the 

 whole apparatus, and 

 its relations to the 

 nerves, are described 

 in the following ac- 

 count of what is seen 

 in the Torpedo. 

 The electric organ 

 (oe) is placed between 



Fig. 277. A Torpedo, with the electric organs dis- 

 sected out. On the right the surface only of the 

 organ (oe) is shown. On the left side the nerve-trunks 

 passing to the organ are dissected out, and part is followed 

 some way into the organ. The cavity of the skull is 

 laid open, and the brain displayed. I Fore-brain. 

 II 'Tween-brain. Ill Mid-brain. IV Electric lobe. 

 v Vagus. tr Trigeminal. tr' Its electric branch, 

 o Eyes. / Spiracular cleft, t Mucous tubes of the 

 skin, br Bianchia? ; on the right they are covered 

 over by a common layer of muscles, on the left the 

 separate branchial sacs arc shown. 



the head, the bran- 

 chial sacs (Fig. 277, 

 hi-), and the proto- 

 pterygium of the tho- 

 racic fin ; it is as deep 

 as the whole body, 

 and is invested by a 

 tendinous membrane, 

 which is covered by the integument above and below. Each organ 

 is made up of a number of parallel prisms, which again consist of a 

 series of elements set in rows one on the other ; these are 

 the above-mentioned alveoli. They are closely united with one 

 another by connective tissue ; they all receive inferiorly the nerves 



