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





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FIG. 124. A. Two electric columns of Gymnotus electricus. (After Schultze.) B. I. Columns from 

 the pseudo-electric organs of Raja clavata. II. a and b. Single segments of I, more strongly 

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

 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. 



