XI 



ELECTRICAL FISHES 



391 



by the appearance of a group of muscles, given off from the flat 

 abdominal muscles, and beginning behind the shoulder -girdle. 

 These diminish rapidly in size, and run as a clearly marked band 

 of muscles below the lateral muscles proper, to the caudal end 

 (M. latemlis imus [me], Fritsch). The lateral aspect further shows 

 this strip to be distinctly curved towards the horizontal behind 

 the ligamenta intermuscularia, so that the short bundles of 

 primitive muscle-fibres stretched between them are presented as 

 low, narrow compartments. It is easy, especially in cross- 

 section, to see that the position of the large electrical organs 



FIG. 255. a, T.S. from tail of Silurus glanis; ft, T.S. from the fourth f of Gymnotus. (Fritsch.) 



of Gymnotus corresponds throughout with that of the band of 

 muscle just described in Malapterurus, which is here wanting, 

 and has by its transformation given rise to the organ. There is 

 no less certain proof that the so-called small organ of Gymnotus 

 has been formed by the transformation of a part of the lower 

 muscles of the fins. In correspondence with the very scanty 

 development of the dorsal fin, two small triangular sections 

 of muscles only are left in the cross -sections of both Malap- 

 terurus and Gymnotus, beneath the skin of the back (Fig. 255, 

 a, &, mp). On the other hand, there are, on the ventral aspect 

 of the cross-section, on both sides from the median plane, two 



