No. 520] ELECTRICITY TISSUES IN FISHES 199 



either end of the fibrils. The less differentiated cyto- 

 plasm has become segregated into a peripheral layer and, 

 owing to the more rapid growth in length of the entire 

 body than of the individual electroplaxes, these latter 

 have become drawn apart and no longer overlap as they 

 did at an earlier date. 



Before proceeding further a word is necessary as to 

 the fate of the surrounding muscle fibers and the way in 

 which the electroplaxes become marked off from the sur- 

 rounding tissues. 



At first the muscle cells that will be transformed into 

 electric tissue are in direct contact with the surrounding 

 muscle cells of the myotome. Then these immediately 

 surrounding fibers begin to degenerate by a peculiar proc- 

 ess of histolysis that strangely enough resembles some- 

 what the formation of an electroplax. The middle of the 

 fiber swells up and the myofibrils lose their striation; 

 lastly the ends are drawn in, the nuclei fragment and the 

 whole mass becomes a lump of amorphous matter that 

 finally disappears. 



The next developmental changes in the electroplax can 

 perhaps be best described by comparing the stage last 

 described with the practically adult electroplax. In this 

 we find that the middle third of the young form has ex- 

 panded into the cylindrical body of the completed stage. 

 The two end portions have failed to grow in size and 

 have become one of the several blunt papillae that have 

 evaginated from both ends. This comparative atrophy 

 of the posterior end of the spindle has left the nerve 

 ending on the posterior surface of the electroplax and 

 on the evagination that project from it, while the anterior 

 end is in contact with a considerable development of capil- 

 lary- blood channels that lie in the electric connective 

 tissue. 



Most interesting in this older stage is the fate of the 

 myofibrils. They have lost their striation completely, 

 the dark staining anisotropic substance seeming to have 

 dissolved and left well-defined fibrils of the isotropic sub- 

 stance alone. These fibrils no longer lie so evenly to- 

 gether although still associated in groups. The wave-like 



