310 



The Electric Organ of the Skate. 



[June 14, 



largest specimens of B. radiata examined there was never any 

 indication of retrogressive changes. 



The small size of the electric organ, together with the shallowness 

 of the minute cups of which it consists, seems at first to indicate 

 that in B. radiata we have an electric organ in the act of disappearing. 

 But when the organ of the species radiata is carefully compared with 

 the organ of the species hatis and circularis, the evidence seems to 

 point in an opposite direction, and the view that the cups of B. radiata 

 are in process of being elaborated into more complex structures, such 

 as already exist in B. circularis, is apparently confirmed by the develop- 

 mental record. Were the electrical organ of B. radiata a mere vestige 

 of a larger structure which formerly existed, we should expect to 

 find the motor (electric) plate incomplete, or only occupying a portion 

 of the electric cup and the nerves proceeding to it, either few in 

 number or undergoing degenerative changes. But instead of this we 

 have a relatively large bunch of extremely well-developed nerves pro- 

 ceeding to the electric plate, which is not only complete, but extends 

 some distance over the rim of the cups. Further, there is no indica- 

 tion of the walls of the cup having ever consisted of extremely com- 

 plex lamellae, such as we have in B. circularis. They consist of a 

 nearly solid mass of muscular tissue, scarcely to be distinguished 

 from the unaltered adjacent muscular fibres. The electric cup of 

 B. radiata may in fact, when its structure alone is considered, be said 

 to be a muscular fibre which has been enlarged at one end to support 

 a greatly overgrown motor plate. But the development of the electric 

 cups is even more suggestive than their structure. Had the muscular 

 fibres in B. radiata assumed the form of clubs before the young skate 

 escaped from the egg capsule : had the clubs been rapidly trans- 

 formed into electric cups ; and had the cups soon after reaching com- 

 pletion begun to disappear, the evidence in favour of degeneration 

 would have been complete. But, as has been indicated, the conversion 

 of the muscular fibres into an electric organ is late in beginning, and 

 the clubs having appeared, pass slowly through a prolonged series of 

 intermediate stages before they eventually assume the cup form. 

 Further, as has already been mentioned, in the largest specimens of 

 B. radiata examined no evidence was found of retrogressive changes, 

 either in the cup proper, or in the numerous nerves passing to its 

 electric plate. Hence it may be inferred that the electric organ of 

 B. radiata, notwithstanding its apparent uselessness and its extremely 

 small size, is in a state of progressive development. 



