270 



GENERAL PHYSIOLOGY 



muscle-fibres (Fig. 123). Each of these columns is composed of 

 transverse discs lying symmetrically upon one another (Fig. 124<,A); 

 these are exactly homologous with the cross-striation of the muscle- 

 fibre, but do not possess doubly refracting elements, and do not 

 undergo changes of form during activity. Still greater is the 

 correspondence in structure of the electric columns and cross- 

 striated muscle in the half-electric or pseudo- electric fishes, e.g., 

 Raja davata (Fig. 124, B). A very interesting and obvious change 



A 



I 



B 



Fig. 124. — A. Two electric columns of Gymnotus electncus. (After Schultze.) £. I. Columns from 

 the pseudo-electric organs of Kaja davata. 11. a and h. Single segments of I, more strongly 

 magnified ; the left half in ordinary light, the right half in polarised light. (After Bngel- 

 mann.) 



of function is here presented, for the electric organs develop out 

 of genuine, contractile, cross-striated muscle-fibres ; and, as contrac- 

 tility is lost, the electric properties come into greater prominence. 

 The similarity with the muscle is also evident during the activity 

 of the completely-developed organ; for just as the muscle in a 

 single twitch gives only a brief current, so in the electric organ 

 the current is momentary, although of incomparably greater 

 strength. 



