Ichthyopsida 111 



The embryonic cells even develop into short and definitely striated 

 muscle-fibers, each of which then undergoes an elaborate metamor- 

 phosis and becomes an electroplax. (The origin of the electric tissue in 

 Malapterurus is not certainly known.) Further, the innervation of an 

 electric organ is such as would be received by striated muscles occupy- 

 ing the position of the electric organ. Caudal electric organs and the 

 subcutaneous electric mantle of Malapterurus are innervated by so- 

 matic efferent spinal nerves. The bulky electric masses of Torpedo are 

 in the region of branchiomeric muscles and accordingly receive branches 

 from cranial nerves V (?), VII, IX, and X. The motor centers for these 

 electric nerves occasion a pair of prominent electric lobes on the 

 medulla. The electric organs of Astroscopus and their nerves are said to 

 develop in very close relation to the extrinsic muscles of the eye and 

 the corresponding nerves. Each electroplax, in all electric organs, is 

 entered by one or more branches of an electric nerve. 



The discharge from the stronger electric organs may paralyze or 

 even kill small animals. Unquestionably such organs are highly effica- 

 cious for defense and in securing prey. In this connection it is note- 

 worthy that the skin of Torpedo is devoid of scales. The value of such 

 feeble electric organs as those in the tails of some skates is problematic. 

 The control of an electric organ is presumably voluntary, like that of 

 the striated muscle whose place it occupies. Mere contact with the 

 body of the electric fish is not necessarily followed by discharge. 



These electric organs of fishes are extraordinary in every particular 

 — the specializing of protoplasm for production and liberation of 

 electric energy; the use of electricity in defensive and offensive opera- 

 tions; the actual transformation, during ontogeny, of young striated 

 muscle-fibers into electroplaxes ; the independent origins of electric 

 organs in widely separated regions of the body, and in several genera 

 of fishes genetically very far apart. 



Transformation of a striated muscle-fiber into an electroplax is to a 

 certain degree intelligible. Contraction of muscle is attended by a very 

 slight electric discharge. In the electroplax the release of electric 

 energy, which is a trivial by-product of muscular activity, has been 

 accentuated and elevated to the rank of the chief function, at the 

 expense of loss of contractility. 



The diverse positions and innervations of caudal, branchiomeric, 

 postoptic, and subcutaneous electric organs preclude any possibility 

 of homology among them. The genetic distance between elasmobranch 

 rays and teleosts is so great that there can be no homology between the 

 caudal electric organs of various teleosts and those of a ray. Even 

 inside the small group of rays appears Torpedo with electric organs in 

 the branchial region, while in other rays the organs are caudal. The 



