io6 



HISTOLOGY 



and in Mormyrus it is well developed; while in Torpedo it is carried 

 to such a degree that the electroplaxes are wide and thin; so thin that 

 layers can hardly be discerned. The broadening and development of 

 the electroplax takes place at one end of the changing muscle fiber in 

 both the ontogeny and taxonomy of the electric tissues, and sometimes 

 the lower end of the electroblast or young electroplax remains attached 

 to the posterior surface. Figure 104 represents a series of diagrams of 



FIG. 104. A -H. A series of diagrams of the various kinds of electroplaxes, showing in part 

 their polarity and their relations to the striated muscle fiber. All nerve structures stippled. 

 Striated structures indicated by lines. A, muscle fiber; B, electroplax of young Raja batis; 

 C, electroplax of Raja Icmis; D, electroplax of Tetronarce; E, electroplax of Astroscopus 

 the "stargazer"; F, electroplax of Gymnotus, the electric "eel"; G, electroplax of Mor- 

 myrus; H, electroplax of Malapterurus. Innervated surface above, on all but G. 



the various forms of electroplaxes, showing their polarity and comparing 

 them with a striated muscle fiber. 



The electroplax is developed, with the possible exception of Malap- 

 terurus, from an electroblast which is exactly homologous with a sarcoblast 

 or young muscle cell, and in some species of Raja are the same, as far 

 as the microscope can reveal. Thus we see that the electroplax may be 

 considered to be a modified muscle fiber whose action produces elec- 

 tricity instead of motion. 



The distribution of nuclei in the electroplax is characteristic; they 

 form a continuous single layer in the electric layer and posterior layer 

 and are separated by regular intervals from each other. 



Each is surrounded by a bit of granular, undifferentiated cytoplasm, 

 much as is the nucleus of a smooth muscle cell in the vertebrate bladder 



