ORIGIN OF THE ELECTRIC TISSUES OF GYMNARCHUS NILOTICUS. 



By Ulric Dahlgren. 



In the seven types of electricity-producing fishes the exact development 

 by which the electric organs and tissues are produced during the creature's 

 life is known in only two, leaving the other five unknown. It also happens 

 that the two forms which have been studied as to the histogenesis of their 

 electric organs are the only two elasmobranch fishes among the seven, so that 

 we have not as yet seen how the remarkable electric tissues in Malopterurus, 

 Gymnotus, Astroscopus, the mormyrids, and Gymnarchus are developed. Also, 

 of the five teleost types we know the structure of the full-grown electric organs 

 in all of them pretty well, except in Gymnarchus. This fish is found in Africa 

 and has been rather rare, so that but two workers have published observa- 

 tions on it, both of them a long time ago and from poorly preserved material. 



It was, therefore, with great pleasure that the writer came into possession 

 of some embryos of this rare form through the kindness of Dr. J. Graham 

 Kerr, Dr. Arthur Shipley, and Dr. Richard Assheton, to whom he wishes 

 to express his most sincere thanks. This material was collected in Africa 

 by Dr. Samuel Budgett some years ago and was in most excellent condition, 

 owing to the great care and skill with which Dr. Budgett put it up and cared 

 for it. The collecting was done unflinchingly and faithfully, under con- 

 ditions of hardship and sickness that few white men could stand, and Dr. 

 Budgett lost his life from exposure and illness incurred in part by this work. 

 A full account of his trip and of the scientific results should be read in the 

 Budgett memorial volume issued by Dr. Shipley, Dr. Kerr, Dr. Assheton, 

 and others in 1907, through the Cambridge University Press (24).^ 



It is somewhat unfortunate that the structure of the electric organs in 

 the adult fish could not be worked up at the same time that this paper was 

 written, but the writer has material on the way from Khartoum and hopes 

 to publish a second paper shortly. 



But three papers have been published on the electric organ of this inter- 

 esting fish, one by Erdl (15) in 1847 and another by G. Fritsch (19) in 1885. 

 Riippel's publication on the subject could not be found, but Fritsch states 

 that Riippel mentioned the peculiar structures which we are considering, 

 and so he stands at present in the writer's knowledge as the first one to have 

 seen and reported to science the electric organs of this fish, although he 

 was in doubt as to their significance. Erdl used a specimen which was so 



1 The figures in parenthesis refer to the literature cited, p. I93. 

 II 161 



