VENOM, ELECTRICITY, LIGHT, AND SOUND 147 



the electric plates run lengthwise instead of vertically, and 

 the nerves supplying them, which may be as many as two 

 hundred in number, arise from the spinal cord instead of from 

 the brain. In the Electric Cat-fish (Malopterurus) , on the other 

 hand, the organ, instead of being made up of hexagonal columns 

 of plates, takes the form of a sheath of gelatinous material lying 

 between the skin and the muscles, and enveloping the whole 

 of the trunk (Fig. 6ob). The electric plates are scattered quite 

 irregularly throughout this layer, and are placed transversely 

 to the length of the body of the fish. There is another important 

 difference, for here the nervous side of each plate is positive, and 

 the hinder end of the fish is positive to the front end, the 

 current passing from the tail to the head. On either side of the 

 body the organ is supplied, not by a single nerve, but by a single 

 fibre; this is much branched, each branch ending in an electric 

 plate. The fibre itself arises from a single, enormous, lens- 

 shaped nerve-cell, situated where the brain joins the spinal 

 cord. 



In the Skates and Rays {Raia), and in the Mormyrids {Mormy- 

 ridae) , the electric organs are quite rudimentary, lying on either 

 side of the terminal portion of the tail as in the Electric Eel. 

 They are, moreover, of comparatively feeble power, and serve 

 merely as a protection against enemies. In the Star-gazers 

 ( Uranoscopus) the organs take the form of two oval areas of con- 

 siderable size, placed immediately behind the eyes (Fig. 47E). 

 These are of a complicated structure, being made up of many 

 layers of electric plates, and are capable of giving off a shock 

 of quite painful intensity. 



How, then, have these complicated electric organs of fishes 

 arisen? In order to answer this question it is necessary to 

 study the development of the embryo or larval fish, and it is 

 found that in the Torpedo, for example, each electric plate is 

 nothing more than a transformed muscle fibre. Further, the 

 whole organs have been derived from some of the branchial 

 muscles, which have been relieved from their original duty of 

 moving the gill-arches in order to take on this new function. 

 The organs of the Electric Eel, the Skates, and the Mormyrids 

 are similarly modified muscles, and owe their origin to the 

 transformation of some of the lateral muscles of the tail. In 

 the Electric Cat-fish the development of the organs has not 

 yet been studied, as the smallest specimens so far obtained 

 have these fully developed and capable of giving a tiny shock. 

 There is good reason to believe, however, that the plates have 



