390 ELECTRO-PHYSIOLOGY CHAP. 



visible in fine transverse sections of Mormyrus plates, " which 

 preserves the complicated cross-striation of the muscle in an 

 extraordinary degree." This forms the middle stratum of each 

 plate ; the anterior exhibits a delicate longitudinal striation 

 (analogous to the palisade border of the Torpedo plate), beneath 

 a fine cuticular border. 



If it is thus certain that the electrical organs so far described 

 are to be viewed collectively as transformed, and specially 

 differentiated, striated muscles, the most superficial anatomical 

 comparison serves on the other hand to show that quite different 

 groups of muscles are in each several case the starting-point of 

 this marvellous process of differentiation. Thus in Torpedo the 

 external layer of the small muscles of the bronchial apparatus, 

 and the external muscles of the jaw which are so marked in the 

 allied ray, are wanting ; in Gymnotus the deepest part of the 

 ventral trunk-muscles, save the small remnant known above as 

 the " intermediate muscular layer," is transformed into the large 

 electrical organs, while the small organs are derived from the upper 

 part of the inner muscles of the fins. In Gymnarchus, again, the 

 electrical organ corresponds with the central portion of the 

 lateral muscles, while in Mormyrus and Raja the parts of the 

 caudal muscles adjacent to the lateral lines afford the material of 

 the " imperfect " organ. The appearance of the electrical organ 

 is not therefore confined topographically to any definite region, 

 but every group of muscles, the normal functioning of which is not 

 indispensable to the existence of the individual, may le held as an 

 adequate substrate for the development of an electrical organ (G. 

 Fritsch, 12). 



If a transverse section through the trunk of Malapterurus, 

 which, as regards its muscles, is nearest to Gymnotus, is com- 

 pared with a similar section of the latter, it is easy on either side 

 to detect the transverse sections of the four lateral trunk-muscles 

 so characteristic of the bony fishes (M. Inter ales proprii inferior es 

 et superior es, Fig. 255, a, b [Ms] and [Mi], and M. later ales dorsales 

 et ventrales, [md] and [mv] of the figures). These, as shown more 

 particularly from the lateral aspect, are divided segmentally in 

 the long axis of the fish by the zigzag lig amenta intermuscularia, 

 the single discs, each corresponding with a segment, being trans- 

 formed into hollow cones, which are, as it were, inserted into 

 each other. Malapterurus is distinguished from other bony fishes 



